The kind of bracket I use for an ossia on the same stem stops enclosing the accidental when the notehead is scaled down, as this clip shows:
This happens at 70% in Bravura and at 85% in MTF-Cadence, so, if I’m using the latter I can’t set the scale at cue size, but in actual fact 85% doesn’t look too bad. But am I correct in thinking that the recourse for scaling below the thresholds is to use text brackets?