Basically, when partner has the 12-14 hand, I expect to do much better at MP bidding 1N. When he holds the 18-19 hand, it make or may not be ok. (Txx does have some benefit oppos. something like QJ tight, for instance) I expect the 12-14 hand to be more likely than the 18-19 hand by at least 4-1, could easily be 10-1...don't know the odds off the top of my head. MP is all about frequency of game, so I think the pragmatic 1N bid is a real long term winner, over some genius bid that will trade many small losses for the occasional big gain...which is fine, even desirable at IMPs, but anathema at MP.