I'm similarly worried about subjecting my P4 to a battery mod requiring cracking the case open. If anything goes horribly wrong, there goes $1400 plus the cost of the mod! No one who has done the mod so far for themselves wants to do any more for others!
What sort of flight times are you getting with your P4? Have you had a 25 minute flight time yet in any mode under any flying conditions? You certainly don't need to fly outside the limited range of the RC to test its potential. Just run a POI around your home point or a manual POI at a faster than 22 mph speed, for testing efficiency for flight time and total distance.
I think you're right. I was talking to chuck earlier about Keith's flight and he was explaining to me that the spot Keith flys starts with 10k of waterfront and Keith is able to fly out at 75 ft for the first 2 miles without having the waste energy climbing and can take advantage of the wind as well. Also I didn't realize climbing with a cold battery kills your battery. I've always started my flights climbing up to 400 ft first and then I start moving horizontal. I'm going to stop doing that now. Guys like you , Keith and Chuck ( many more) are great to pick their brain and learn little tricks . I've only been flying long distance flights for 9 or 10 months so I got a lot to learn .Keith might also have just been riding a tail wind in both directions, if the wind shifted at the perfect time. However, from the log, you can see that the 5.68 mile flight out was completed in just under 12 minutes, so 5.68 miles x 5 = 28.4 mph average and the total flight would have been completed in under 24 minutes with 6% remaining. I'm got 25 minutes on my first new P4 flight in P-GPS. 28.4 mph may, in fact, be the real sweet spot in P-GPS, with OAS off!
"Climbing with a cold battery kills your battery"...literally! That's what crashed my beloved original W323 P3P! Flew straight up to 220 feet and one cell tripped 2.99V under the load, and shut the battery off in midair! DJI GO showed 86% remaining at launch! Battery had not been topped off and had started to discharge and the cells were no longer properly balanced. I did not use the externals which were attached, because this was a quick test flight with a unmodded battery, and I didn't want to waste them. Lesson learned!
At least we don't go down with the ship, testing the limits! 
In my initial testing with my original P4, flying in Sport mode was worse than flying in P-GPS with OAS off, because of the faster speed in Sport mode. However, oddly, and I say oddly because DJI claims their 28 minutes was in ATTI mode, ATTI mode with OAS off was the very worst of all! I flew full throttle in all three modes with OAS off, and only got 12 minutes in all ATTI, and 16 minutes in P-GPS, and 15 minutes in a mixture of Sport and P-GPS.
Those are really poor results. Have you checked your batteries in healthydrone . Have those numbers improved any at all.
Yes, significantly, but not without changing a few settings. New P4 got 25 minutes first flight in P-GPS with OAS turned on to limit speed to 22 mph. Second flight in Sport mode, I flew for 6 minutes until 8 minutes remained on flight time, when I switched to P-GPS, and squeezed another 12 minutes out of it, getting 20 minutes total.
There is no doubt that the stock P4 transmitter has the worst range, at 20% less power output than the GL300A and GL300B transmitters sold with the P3P and P3A. The additional reduction of 20% in video power from the P4 aircraft over the W323 P3P certainly isn't helping FPV stability at long range either.
I have owned two P4's, and the first was returned to DJI for refund, and the second was acquired last week. Same lousy stock RC range on both. No biggie. I have paired both with my FPVLR v2 boosted GL300A, and easily get 3+ miles. I also have the DBSv2 mod on another GL300A transmitter. Anything is better than the stock P4 RC. My P3P flies out 5.2 miles with full signal and FPV at 100 feet.
That's weird. I was afraid and kept a p3 just incase. But I have to say that I have defiantly noticed an improvement. Also, what's a stock remote lol?
I thought the same thing so I bought a gl300a controller for my p4 but I got slightly less range on a couple flights and exactly the same range on about 6 flights . I flew from the same spot each time and the same flight path. I would link my a controller and run 2 batteries and then charge and link my C controller and repeat . I basically got about 1000 ft less twice and the rest were equal give or take a couple hundred ft which that could've been my aiming. My average distance was about 8k ft stock. So I modified my C controller that came with my p4 with the maxxuav.com dbs setup. The results have been great . I can't out fly my signal but I'm still trying to figure out the best way to fly this p4. But many people have had better range with there gl300a controllers so I'm not sure why mine didn't.
Odd. I suspect it's a quality control issue. I knew my original GL300A had awesome control distance of 3 miles, back when DJI only advertised 1.3 miles. I treated it like gold! I bought a new GL300A that was already modded to not have give up my original GL300A. However, once any of the controllers are modded, the original power difference in the stock units basically becomes moot. My stock P4 controller, even with a windsurfer, craps out at 6,700 feet at 400 feet AGL. Without the windsurfer, it loses signal at 2,500 feet. Paired with my FPVLR v2 boosted GL300A, I got well over 3 miles, but had to turn around because of battery life. Now that I know how to get 25 minutes out of the battery, I can safely push the control range past 3 miles. Keith got 5.8 miles!
Still need a P4 battery mod, though! 
. Very strange.
