First of all, this score system is amazing and it really changes the gameplay to the better in many ways.
A couple of things to think about though (I do not know if any of these things is the case already).
In general, not always (as it should still matter how much hp you take away):
- It should be
more worth it killing someone rather than damaging someone
- It should be
more worth it killing a rider than a horse- It should be
more worth it damaging a rider than a horse-
If you get the kill, the damage dealt shouldn't matter as much as if you just damaged without getting the kill
I also think that killing a riderless horse should give a minus score.
Not much, but enough for a player to reconsider it before just instakill a horse without even looking around if some teamate might want to mount it, which often is the case.
This will only improve teamplay while at the same time decreasing the risk of anyone killing a horse or any other animal IRL...