I have 2 custom built flint locks and shoot year round, in fact I shot Friday afternon and yesterday, it was in the mid 80s...I can't see a difference...I have tried different patches and lube and have seen this make a difference...

You mentioned the recoil, heavier recoil will kick the ball higher...Are you sure you are using the same powder charge, patching material and lube??? Also, do you clean between shots, the extra fouling can also give more felt recoil...