Wont play much more today but I'll be working some sums for bb v sb. Lots of sb limpers and I tend to raise to 3x virtually any two there if they've shown they can fold. I need to find what to raise in the bb when they don't. Presently it's any two both higher than a 9, but I read that somewhere so I'm not considering it legit without the theory.
Yeah I don't have the theory behind this either, just know that I have multiple default ranges that were given to me by my coach. A couple things to consider when you are in game or while you are doing your off table work. First, is the limper a fish or a reg. By that, I mean are they limping because they are a rec player and are just trying to see a flop and make a hand or are they a reggish type player that is employing a SB complete strategy. Can't say that I have run into the latter on MPN. So I have a range for both of those. On the rec player range I have 2 sizes as a rec player isn't going to exploit me. The other thing to consider, if you have this info, is what is their VPIP and PFR. I 20/10 rec player limping the SB is completely different than a 70/30 player limping the SB. You still have to consider what their limping range could be and then what hands can you raise for value against those ranges.
Good luck!!