I suppose I need to know what people’s experiences are of riding frames that are too small for them in the standover but they liked cos of the cockpit.
I ride a 20″ O-O fatty, they all have the same standover form 16″ to 20″, and the TT is dropped even on the 16″ so it’s around 14″ center2center. Apart from the obvious gonad clearance there’s nothing unusual about the way it rides. The only downside is it’s a PITA to lift over stiles etc as it can’t be shouldered comfortably. TBH I don’t really see why any bike needs to be bigger than a 16″ frame except for bikepacking, with a seat-tube brace, small, medium, long and extra long, rather than small medium, large and XL.
There is an argument on L an XL frame that the chainstay needs to be longer and ST steeper to stop the saddle going back over the rear wheel, but that shouldn’t be an issue on 16″-18″ frames.