I found the other half of that bit I cut off:
A bit out of focus. In this picture the top is actually the bottom of the CS (you can see the rusty dropout) and where the brazing flowed in the best. There's a sort of cap on the end of the CS with a slot in it to make a nice rounded junction with the dropout and it looks to me like there's a fairly decent amount of braze flowed in around there. It looks like the bottom (the top in this picture) was touching the inside of the CS so had a good fit for the braze to flow into that joint. But on the top the gap was a bit too big.