I think that is because :
16 dbm is for CE 40mw [safe]
20 dbm is for FCC 100mw [safe]
27 dbm is this mod 500mw [ safe or not ? we need to test it ]
if you want to go with FCC power , go on 20 dbm
if you want more , go with 27 dbm
personally ive modified watchlog.sh to have 2400 in settings (...