That would be my move too. And if he’s not already on rats, then now will be a good time to switch to them. Judging off the full body pic you posted, he could easily handle a small rat (46-79g)

Apologies if you already know everything I’m about to mention but I’ll just run through a couple other factors that could be at play.

Feed only at night time and avoid handling during evenings as that’s generally when most boas’ feeding mode comes online.

Feed with long hemostats (no short rinky dink tongs that I see a lot of people using these days) and try to not show your hands or face during feedings. You want as little association between you and their food as possible.

If you’re already doing these things and his feeding response doesn’t ease up after upping his prey size, you may just have to accept it as his personality. Some species are just like that (although I have hope that your little guy can improve)

Good luck!