I like the 3b pre-flop, you are not committed to anyone and MP1 now has to make a decision for all his chips given his stack size. He can't just 4b/f in the spot you have him in.

I think the cold 4b here is likely to be very strong for a few reasons:

1. He is committing himself to calling a shove from you or the opener.

2. He is OOP which makes it very unlikely he would offer compelling odds preflop.

3. I think even hands as strong as JJ / AK would either shove or make a bigger 4b preflop due to vulnerability.

4. In a $10 MTT the chances of someone 4b bluffing in this way are probably remote.

The call of the 4b is probably a bit loose. I think if you call in these situations and make a pair + backdoor flush draw then you have to go with it against a 20bbs stack otherwise you are spewing chips as the opportunities to proceed on the flop are going to be pretty limited and even when you do proceed you are crushed a lot of the time. 

I think the cbet sizing of 40% is pretty common on a dry board with his air and big hands and having called preflop I kind of feel compelled to call at least one bet but again that gets awkward as you are probably committed then.

I had a similar hand a while back and ended up calling a small flop bet and feeling pretty uncomfortable. As it happened, villain had QJ and paired his Q and I paired my K. I felt it would be too weak to give up there and then but wasn't happy about it! These are tricky spots and can probably be avoided by folding preflop having only invested a small amount.