Would it be possible for you to post photos showing how close your exhaust is to your starter? Include far away and close up photos.
Is it possible to fabricate a sheet metal piece to shield your starter?
Instead of wrapping the starter, first try wrapping the exhaust with heat shield wrap.
Look here:
https://www.youtube.com/watch?v=s4U4b7lifF8
Also: Google Heat shield exhaust wrap for more info.