Thanks for the shim idea, I may give it a try. Nothing to lose. I don’t think I am measuring incorrectly, I am using a digital caliper. Thicker at the top and bottom of the drops (22.2mm), but slightly oval (as measured) through the bends. I thought it might be a function of the age of the bike - thinner handlebars in older bikes.

I will certainly check out Veno Orange. Maybe cheap but cool looking replacement brakes just don’t tighten correctly and I should try something else. I’ll try it on a piece of PVC so I can see if the band actually moves and tightens!