I think the custom frame builder world places too much importance on tube-to-tube contact. It's clearly best practice, and every builder of high end frames should aim to do so as it is the superior way, but the actual evidence points against it being strictly necessary. Many, many decades of production frames were built with unmitered tubes usually signified by a large lug socket for the TT/DT, or with poor miters and more "normal" looking lugs mostly just to maintain lap braze surface area with little regard to the butt braze portion. Given how little tube-to-tube contact there actually is in a lugged shell, and the fact that many high end builders historically didn't even bother to miter at the BB since there's no tube to butt braze against, it's clear that the strength of a lugged BB shell is mostly in the shell itself and the brazing in the sockets. With the right lugs, you can make a joint without miters. With good miters, you can make a joint without lugs.