Do you have wildlife that could be eating the flower buds? Bamby loves to eat rhododendron and azalea flower buds and that might explain why you get little bloomage near the top of the plant. They nibble on the top part and a little or very little on the bottom part depending on Bamby's preferences and height. On the other hand, if the azalea were to bloom fine on top but poorly on the bottom, I would have suggested rabbits as a possibility. Squirrels can also eat the flower buds when they are hungry.
No, not really. I cannot think of a soil or sun problem that would affect/reduce blooming only on the top of the plant. That is why I suggested some common pests.
My azaleas in the back get sun either in some parts of the shrub or all of the shrub in the morning; then theyy get shade in the afternoon. Other azaleas in front of the house get no direct sun at all times (but get plenty of indirect sun). Neither tends to bloom mostly on the bottom part.