From my personal experience, vatf will be constantly harassing the gatf regardless of size difference.. almost all the gatf I've kept together, they seem to comm alright just fine if you have another alpha/peace keeper tank Mate in there. I had my vatf at the bottom of the hierarchy and right after I introduced some gatf, he/she started bashing on them relentlessly.. that very same vatf eventually got taken out by a dorado probably half the size or even smaller....