Hi there Toby, welcome to the forums.
I dont think they are to high given the position of the viewing seat in relation to speaker.
With direct radiating speakers of the type you have it is better to mount them higher and angle them so they fire across the room (just as yours are). This usually gives better results as the sound wont seem to be coming from one point in space, and the whole idea of surround sound (on movies anyway), is to create a more "atmospheric" sense of sound coming from behind you.
If the speakers were lower (head height for example), you would find they would make themselves more noticable and not create a sense of space to the sound.
If you were using di/bi-polar speakers (as I am), then it is better to mount them lower (mine are approx 12" above my head when seated), and fit them to the side walls in line with the listening position.
As I have an AVR cabable of 6/7.1 surround I also have a pair of bi-poles on the bookshelf behind the sofa (not an option for you looking at the photo of your room).
In short then, I can see no reason to be concerned about the positioning of the surround speakers. Try repositioning them temporarily if you think it may give you a better sound, bit I think they are OK where they are now.