Here is my exercise that helped me improve a lot in this area! Hope it helps :)
Yes! That’s is totally normal, it took me quite a long time to be able to see my distances and even longer to be able to see my distances on different horses. A very good exercise would be to practice I’ve poles or small cross rails, that way you don’t have the pressure of finding the perfect distance to a larger fence. Counting the strides out loud really helps me when trying to find distances.