This is not a direct answer to your question, but this is what I did to NOT have to buy another fin. The heel strap is 1/4" bungee and is easily removed. I wear a 10 wetsuit boot and a 11 rock boot (to go over the dry suit sock) and have medium novas. The rigid sole and toe still goes up into the fin pocket, but the strap was too tight. I just cut a longer bungee and replaced it in the fin strap. Since the toe of the rock boot goes into the pocket, but only up to the instep. Your ankle is supported with the laces, the sole propels the fin and the longer strap keeps everything in place... I swear it is more comfortable than just having wet suit boots and a closer pocket fit. Seems like the rock boots transfers the load from the ankles to the leg. The rock boots counter some of the floaty characteristics of the fin. Give it a try... It will only cost a couple of bucks. You can carry your shorter bungee for a switch-out when wet suiting. Always a good idea to have a spare anyway.
