You are comparing two different energy outputs. .4 at 380 fps is equal to about 2.67 joules, but you're comparing that to 400 fps with .2, which is only 1.48 joules. So your gun with .4 at 380 fps has to be compared with an AEG that shoots 536 fps with .2s.
To maintain the same energy, you should be aiming for ~280 fps with .4s