Custom swim stroke length (open water)?

I'm a terribly slow breaststroke swimmer. Watch permanently under water, so no GPS tracking. But to my surprise, the Fenix 6 does get distance during OW swimming. That's awesome! However it seems to assume that I'm a good swimmer, because it overrates the distance quite a bit. I wonder if there is a way to set a custom swim stroke length, as there is for stride length? I can't find it in the manual, so probably not, but just in case I missed something, I'd like to hear if there is a way.