The fillet brazing is super smooth - there's no obvious butting my inexperienced eyes/touch can tell. But I've just measured it below the top tube/seatstays and it's 28.6 so that would make sense then, I think i.e. 30mm above because of the butting and standard below? Thanks for this, very helpful.
Zona ones are 1.2mm wall thickness at the top, paint could account for the extra 0.2mm.
You should be able to feel if not see the butting.