I am unsure of what you mean during a side split, but if you take the description and apply it to a side kick you are basically dividing the energy of the kick with an improper angle.
If you were to do a side kick, the alignment should be in a direct line from heel of supporting leg, to shoulder, to hip, and finally to heel of kicking foot.
If you tilt the hip forward to accomodate the kick, your alignment is off and thus less power is focused int the kick but distributed to the forward tilt of the hip.
This generally means that you still lack flexibility and are compensating for the stretch of the leg by moving the hip, and thus the torso, forward.
I am unsure if this is what you are sort of describing, but hope it helps.