He isn't overweight. If anything it is hard to keep weight on him being a 13 year old OTTB. It seems he's sore on his toes not his heels. When he walks he is landing in a heel first strike. I imagine, if his heels were sore, he would land toe first... I might take him off the BOSS for a while and see if he improves.
Will his foot eventually be drawn back up into the capsule better? I see what you are saying about the dip. Makes sense now that I know more about the structure of the hoof.
Hubby will be home for the weekend and I'll have him help me get some better pictures. Sometimes it's hard to make a horse and my 3 year old son behave at the same time :)