For these test joints I'm going to use a light weight, high strength fairing compound to add small fillets to the tube joints. The theory is that the carbon won't be making sharp radius turns when it's compressed against the joint. I know "filler" is frowned upon so we'll have to see how the joints perform with it. The photo below is as it was applied, prior to sanding. When finished the fillets will be less than 1/4" radius and the tubes clear of excess material.
The filler used in all the joints depicted below weighs less than 12g prior to sanding.