Didn't try the mod yet, downloading it.
However I am reading your readme file at the repository and stumbled upon this:
or that an horse archer could rode with no hands an horse without any penalty to his maneuverability?
To that, no I don't think it is strange at all.
There is a way to make the horse turn using the body language. A horse is a flock animal so when you ride you can apply pressure from you left knee in order to "push" your horse to the right. This is the same principal as when horses run in a flock and the flock turns then many horses push the others, hence the reason they understand the body language like this.
Of course the effectiveness depends on the understanding between you and your horse. (so stubborn type should have a penalty there)
Also I have no idea how this could be used to warhorses or chargers since they have armour and will most likely not even feel your push. Finally I don't know if there is an effective way to stop you horse without the use of hands.... maybe verbal command, don't know.
So anyway I suggest you do not give penalty to the turning... or at least not to an experienced rider who knows the body language (above 4 perhaps?)
So decide for yourself if you want to rebalance or not, just my 2 cents