I'm just curious. Do you tend to overthink your riding? I ask because many horses can navigate smaller jumps just fine without much input from their riders. It's when the rider starts to anticipate the jumps, gets all figitey up there and impeeds the horse's jumping effort that things start to fall apart. I recently had a horrid jumping round. We got deep to everything. My saint of a horse jumped it all, but I buried him to every fence. Sure enough, when I saw the pics, my upper body was way too forward. He wasn't able to get off back himself off the fences because I was already jumping for him.
My point is, before fixating on counting strides or anything intricate, make sure your position is consistent and correct. Riding forward over the horses shoulders almost never comes out well, and riding defensively makes for lots of runouts and dirty stops. If you're still trying to manage strides 3 strides out, it's too late anyway and you'll only be interfering with your horse who probably already has it nailed.
Here's my exercise to prove to you that your horse can do it by himself. First find a yardstick or use a tape measure to mark out 3'. Then figure out what 3' is to you so you can walk it consistently every time. Once you can walk that, then set up your poles. Just place them in distances in multiples of 12'. (use multiples of 11 if your horse's canter stride is on the short side) Then pick up a canter, get into your half seat and practice cantering the poles without doing anything except providing a release when you cross the poles. Just your arms move. Nothing else in your upper body. Don't look down. Just gaze ahead over the next pole. First practice it the 'doing nothing' way. Your horse will probably have little to no problems doing it in the 4 strides.
Once he's got it the 'doing nothing' way, try and do it for him. Do whatever you've been taught to do to adjust his stride to get the 4 strides yourself. After you've completely frustrated yourself on trying to see the distance and your horse tripping over the second pole, go back to doing nothing and watch it all come together again.
Sure, eventually you will need to see strides, but I'm guessing right now you're prone to overthinking. Seeing distances is something that starts to come on its own once the more basic things become more automatic. By basic things, I'm talking heels down, knees not pinching, back straight and supple, shoulders open, head up, eyes ahead and proper release. When all that basic stuff is good, move onto distances!
You just have to see your distance...you don't have to like it.