Actually height of the rider does effect suitability because it effects the balance and the ability to give cues. However, its the horse's height that doesn't matter so much, but rather its build. A tall rider can be fine on a stocky horse no matter if its short or tall, but that same tall rider on a very fine built horse will not be able to give proper cues and will have a harder to balance.
However, this horse and rider look to be well matched.
Hard to tell from the angles and also if you add tack you might look different again, but from those pics he looks like he is decently solid and you look very fit yourself, you both compliment each other well :)