That sounds rather strange. changing to a lipo can't make any difference in the servo throw. all you're doing is applying power to the electronics and the throw should be exactly them same...

anyway, when my son and I changed to lipos, we adjusted the blade pitch so that it was zero at low throttle (with the fly bar level)....this setting flew the heli ok, but we needed full throttle for lift off. we then adjusted blade pitch by one half turn at a time on the clevis until we could get into a hover at about 70-80 percent throttle. it took a total of 1 and 1/2 turns of positive pitch to do this.

So I suggest a simple increase in blade pitch...see what that does..