The entire foot is weak so every structure is "misshapen" - including the frog. With time, as it becomes healthier, the shape of the frog will also change to what you are more accustomed to seeing.
Keep trimming him correctly and get his diet as balanced as is possible so that he has all the building blocks to grow and repair his hooves. Then just wait for the hind feet to heal and become stronger. The good thing is that the hind feet normally respond much more quickly than the fronts as they are usually healthier so you should start to see positive changes quickly.