the ring of the bit has a minimal effect. the bit itself is more likely to affect a behavioral reaction.
How do you know his palate is scarred?
If you need a bit, try a double jointed snaffle first He may prefer that. Also, not too thick for his mouth and don't pull it up too high. skip the old 'two wrinkles ' adage. One or NO wrinkle may be more comfortable for him.
maybe he will prefer a solid bit, or even one with a bit of leverage.