Wire width matters
If the wire is already too wide, sister sizing may not fix the real issue.
Bra sister size charts
Different brands label the same step a little differently, so keep the fit logic in mind instead of memorizing one rigid table.
Soft cups behave differently
Bralettes and wireless styles can tolerate band swaps more loosely than molded cups.
Check support, not just closure
The right sister size still needs the band to sit level and the straps to relax a little.