Here's an interesting chart/info based on research done back 100years ago. Notice this is butt joints with silver, not lap joints (ie lugs) but I think it gives at least some indicator of the dynamic going on with bigger gaps and how strength gradually drops away. The point I take away is that a tube fitting fairly snugly (.003" or less) is very strong and easier to make nice shorelines. I'm not saying .003 is what you should aim for but, that's a fairly snug fit and even tighter is ok it seems. I think something that tight for brass would prevent it from flowing but I don't know that.

The Famous Joint-Strength vs. Joint-Clearance Chart - Kay & Associates Brazing Consultants

I would be interested in hearing from Doug or Mark on the idea of putting a layer of nickel silver around the inside of the socket and then grinding to get the fit you want before brazing it up with 56% silver.