Straps shrink and stretch over time. A 22mm will squeeze in and be fine. I found via my interest in canvas straps that case and strap dimensions are not precise. Eg my PRS-5 Broadarrow has 19mm lugs, except they are actually a fraction larger at 19.12mm. Then take a 20mm Haveston, actually slightly under 20mm, and the difference is then minimal and the strap will fit ok. More critical is the gap between the spring bars and case, if this is too tight then a leather strap will rub and be marked, perhaps even marking the case.