this would probably be very harsh on lancers, since almost every stab with riding speed is above 30dmg.
people would just start using another polearm instead, makes no sence to loose a lance with 1 stab (gamewise, RL doesn't have a say in this ^^).
If you would decrease the attack angle a little, that would already give lancers a big difference, making it harder to use the weapons length against fx 2h, since you have to account even more for the "weapons lengh - [length from horsesfront to lancers hand]" ratio.