Dan made a good point (one of several) about putting perches for him to stand on while he eats. I have one of those cactus wood types between Timber's bowls (One for pellets and seeds, one for fresh food). He will always stand on the perch, reach over, get something then stand on the perch to eat it. The perch is about level with the top of the bowls. His water bowl can be accessed from the long perch (similar to the one in your pic). He will stand on the edge of the bowls once in awhile, but most often he stands on the perch to eat or drink. The perch you have on the outside for him now looks a lot more comfortable!
I am not sure what you mean about not being able to move the perch. It you take that nut you can see off the end, you can move it? You don't take the screw out of the perch.