Well first of all we are speaking about interlude.
There we go...i know that if u have 3 lvl difference between the RB and urself the drop rate is decreased . BUT does that happens in epic rbs also?for example AQ/baim etc?rly need an answer from some1 who is 100% sure

If the files are l2off or working correct, it is as you said it - 3 lvl max for optimal drop. This apply for every raid and mob.

Ok i got than but..how can u explain that for example valakas 85 lvl RB has 100% necklase drop from 80 lvl chars which is -5 lvl .

If you are higher than the RB by 3 lvls the drop rate its affected; if you are lower than the rb with 65 level sthe drop rate isnt affected.