I use mini roman in my 2/1 structure. I used to use it promising a 4 card spade for the basic premise that we all, or shall I say, most of us, bid aggressively. Since 2nt is the only game forcing bid, if your singleton was spades, the bidding would go... 2d 2nt 3s There are a series of hands which could then make this an awkward auction. Opener could be on the light side and although responder has 14, can't make any game bid. Responder cannot shut off at this point since opener is game-forced. Responder could be 4234 or 3334 headed by the Qs -- scratch 3nt with an 11-12 pt opener hand. I've recently employed using mini roman with having any 4441 and either 4405 or 4450. Furthermore, I use the submarine method for identifying the singleton/void (bidding suit below), which offers more room to bid. Responder can make a cue bid asking what range and if you have a void.