Wow Soot-she has really evened out! She looks like she is stood on a slope in that first pic
Goose rumped is not the same thing as a jumpers bump ..or so i thought...
A jumpers bump is formed when there is a strain or tearing of ligiments around the sacro-illiac joint. Either from over use, or sometimes caused by a fall. Not something a horse is born with like a goose rump.
Oops, just realised I answered the wrong question! Sorry lf!
Bum high means a horse will find it harder to raise the back and lift weight off the forehand. It often gives a kind of downhill conformation which can mean the horse is heavy in front and won't find it as easy to shift weight back onto the quarters as a horse who is more level. Again, it's sometimes seen in draft types who are basically built to lean forewards into a collar and pull.