While we can get a hint at some of the factors in play by watching the horse move, studying how its hooves land and looking at its conformation, that in itself is only superficial.
The only way of guaranteeing that the balance is right is to have detailed knowledge of every injury that the limb - and indeed the rest of the horse - have undergone. To react and allow for every stress and compensation that the limb - and the whole horse - have to make as a result. To allow for micro-trauma to tendons, ligaments and muscles that you can't see and have no way of monitoring on a regular basis. To factor in a response to the terrain the horse lives and works on and to adjust growth so that is is appropriate for the level of stimulus the horse is getting.
Don't forget that all of these factors will change from day to day, week to week, season to season - and you begin to get an inkling of why balancing hooves is an incredibly complex job.