The string type, and gauge have everything to do with "flop"
Yeah, I think it's more to do with strings than anything else. As for the tight neck pocket / stiff neck theory, I just don't buy it. Unless the neck is so bad it's constantly moving everytime you pluck a note I don't see how this could affect 'floppiness' (is that a real word?
).I also think it's much more about string quality than scale length. The very best B string I've heard is a 128 guage LaBella (Slappers are the very best but hard rocking steels are also nice). Much better than any 135 I've tried. I also think that the thicker a string gets, the less usable it is higher up the neck, with all sorts of nasty overtones.
As for a tight sound, plucking softer will help, as will having pickups in the 'turbo' position closer to the bridge which emphasizes the low mids. Think Smith, Roscoe, Stingray, all of which have great sounding 'tight' B strings. In my opinion, scale length will give more tension, but it's only one part of the equation.