A: Every horse is its own story, but there are some fundamental boundaries to being assertive.
First, do not try to be a hero the first time you shoe a horse with this problem. If I tell myself that one thing, I usually will surprise myself with the results. But if I don’t, I’ll tend to overtrim the bottom and any flares or place stress on some other part of the horse.
Ask the horses some questions. Watch them move. Try placing a wedge pad under the horses’ feet (forward and backward) as they stand. Usually, if they like the pad, they will stand on it and even lift up the other foot; if they don’t, they will step off of it. Watch what happens! You’ll miss more by not looking than by not knowing.
As far as breakover and heel length are concerned, keep it simple. Trim the feet to their proper proportions and shoe for balance and form.
If you are unsure of what that is in these situations, I suggest finding a Bob Pethick clinic. I have yet to see a better presentation on the effects of trimming and shoeing on these high-low horses. The photography is awesome and indisputable.