You can start with a contract of 8 strides, and then increase the amplitude for 7 strides, then 6...
The regularity of the paces - necessarily learned while training on the flat - must be maintained when riding over poles on the ground. The same applies for the possible variations of the canter: lengthening and shortening the stride.
During this exercise, the rider must concentrate on the quality of the canter when approaching from a distance, throughout the exercise and also when landing after the last fence. One may or may not allow the horse to change legs; what is most important is to remain straight and jump the poles or fences in the middle. In doing this, be as precise as when riding a dressage test.