Howdy,
Yeah, agreed with Mike about that shin not being wide enough for you.
If it were me, I'd break out the heat gun and a cylinder with a little bigger diameter or something to form the plastic a bit and see if I could make it a little wider. Might end up destroying the pad if you goof it up, but its not like its working for you the way it is, so you don't have a lot to lose... I would remove as much padding as I could easily, heat the whole pad in the areas where I wanted it wider, then press it down onto the cylinder and keep it there until it cooled. I would use just enough heat to make it a little more pliable. If it 'sprang back' after cooling, I'd heat it while it was on the cylinder/form.
Mark