This is one of Madam's hind feet in close up and prior to trimming. The second picture is with half the foot very lightly rolled and the other not yet done.
The close up shows (I think) the tight white line in the forward part of the foot and also the chips that are appearing in the outer wall.
There is no wall height to remove, I just keep rolling out the flares and chips as they occur. I tend to touch up once a week/10 days, doing just a small roll rather than anything major. If the toes square off I roll the rest of the foot to match. Next time I might put in tiny quarter scoops all round. These feet seem to need them and they have worked a treat on the Grey.
But being very cautious I only do a very little each time and then monitor physical performance and how the foot grows afterwards. The horses are very honest. It seems to me that even as I put their feet down they instantly give feedback on how I am doing.
Madam is getting better all the time, but I admit to feeling frustrated that she doesn't have better concavity and is a long way from rock crushing.