If someone is riding a pony in the beginner division (2 ft, horses and ponies not separated) would you prefer to see an add in a line or the pony really motor to get the horse strides? A large pony, whose stride is around 9'-10', not a small with a teeny stride.
I'm not so worried about the exact number of strides in a beginner division. I'm more interested in consistency. So if a pony has a healthy-looking (not crawling) canter, and it adds one safely in each line, it won't bother me in that kind of division.
If the course is twice around the outside, ideally the pony or horse should do the same number of strides both times it does a line.
At the schooling shows I've judged, I'd be happy with whatever it did as long as it was safe and consistent. A pony that ads three away from the gate and makes the strides towards the gate is bad, as is a pony that is going so fast it appears unsafe in order to make the strides.
In our local show series, which actually can be reasonably competitive, I have never seen strides matter. I took my green horse there and added one to each line for the first couple courses. He is horse sized but we kept a consistent, reasonable pace, and went for the adds so he didn't get flustered. In these shows, particularly if there are ponies showing against horses, I cannot imagine that they will count strides against you except in an absolute tiebreaker. More often than not something else will separate rides.
Horses at 2' normally add one if the lines are set for 12'- no jump to take up 6 ' in the air on either side. Ponies in novice classes usually do the add at 12' and a double add at lines set at 10 or 11. Safe and smooth trumps the math.
When opportunity knocks it's wearing overalls and looks like work.