I'm curious: what's your boot sole length? Phil - or somebody else - can chime in here, but I believe longer boot sole lengths can affect ski feel. Probably because the longer sole effectively places the ball-of-foot a bit further back - and perhaps making the ski's sweet spot a little harder to access.
I have Raptor RS 140s, 28.5 mondo size, and around 325 sole length. I too tested skiing Rallys and Titans with the bindings moved forward a bit. I found I liked them better set 1 to 2 clicks forward. I haven't noticed any increased tendency for tail washout - but I'm not an 11 10ths skier either.
My BSL is currently 316 (mondo 27.5). My feeling is that my weight is better balanced now along the ski length overall, and the couple tail washouts weren't anything spectacularly bad. Just surprising because these tails are flat an a little wide and if anything, they hold, They still do, and, to be sure, my weakest link right now is stance (need to be more forward) and separation. So, some of it might have to do more with my limitations than my body build.