Look at the fence all the way round the corner, keep focused on the top of the fence, count your strides and then feel where you need to be.
LOok at the base of the jump
I try to work over poles as much as I can either related or not. The more you engage your eye and the repetition of the poles the easier it is when you apply it to fences. Just try to keep your minds fresh and not do circle after circle to include the pole, make it so it’s just in the way of your line.
At our barn twice a weeke we put poles on the ground and 4 long strikes/ 6 very short strikes in between it really helps keeping your eye on even if you don’t actually jump
I currently struggle with that too, so before you put up the jumps or just on a flat day, work on finding the distances with the poles on the ground.