Horses have such crappy maneuver, cav is commited to an attack 2 seconds in advance, which is huge. Targeting people dead center is the only way to reliably hit them with something, be it your horse or your weapon. With current horse stats, that simply does not depend on the rider.
Of course when they are not playing attention at all and nobody else is putting you in danger you can slow down and make things a little bit easier, but that is quite a rare occurence.