For trot poles I usually go 4 foot spaces (heel to toe) then the poles on either side. And for canter just 4 regular steps :) the stride will change/ regulate for each horse so set it up and go through it and you may need to just tweak it a bit 😊
Trotting poles for a 14.2 are generally 4foot part and canter11
I use trotting poles at 1.3 - 1.35 m and cantering poles 3m but sometimes, 2.7 too, but those are harder for us.
I use trotting polls 1.45 meter between them and cantering polls 3 meters to make normal canter. You can change the distance little bit between them depending in what you want to work!! 😉