From wiki to help you understand what you are looking at.
The croup is from the lumbosacral joint to the tail. The "hip" refers to the line running from the ishium of the pelvis (point of the hip) to the point of the buttock. While the two are linked in terms of length and musculature, the angle of the hip and croup do not necessarily correlate. A horse can have a realtively flat croup and a well-angled hip. Racehorses do well with hip angles of 20-30 degrees, trotting horses with 35 degrees.
Steep croup but fairly long "hip".'Steep Croup or Goose rump
A steep croup is often linked to shortened stride
Less of a fault for slow-moving horses such as draft breeds than for light riding horses
Flat croup.Flat or Horizontal Croup
The topline continues in a relatively flat manner to the dock of tail rather than falling off at oblique angle at the hips. Seen especially in Saddlebreds, Arabians, and Gaited horses .Encourages a long, flowing stride. This helps a horse go faster, especially when a flat croup is sufficiently long to allow a greater range of muscle contraction to move the bony levers of skeleton.
Short croup
Length from L-S joint to dock of the tail is insufficient for adequate muscular attachment
Reduces power of hindquarters .Usually seen in conjunction with multiple hind leg faults .
Short "hip"
The L-S joint is often behind the point of hips. Insufficient length from point of hip to point of buttock
Horse will have difficulty collecting. A well-muscled build may hide a short pelvis.
Provides less length of muscular attachments to the thigh and gaskin. This diminishes engine power in speed or jumping events. Short hip is less effective as a muscular lever for collection and to contract the abdominal muscles as the back rounds. More muscular effort is required.
Flat "hip"
Flat pelvis, line from point of hip to point of buttock flat and not properly angled, result is pelvis structure too long. L-S joint often tipped, ishium improperly placed. It is more difficult to engage the hindquarters, so the back tends to stiffen. Thus it is hard to excel in dressage, jumping, stock horse work. Minimizes the ability to develop power at slower paces needed by draft horses.