Originally Posted by Andrew R Stewart

Brazing a bottle boss is dealing with a huge difference of contact surface area, WRT the amount of edge between the two parts. meaning that the boss has so little area to have the filler flow into and has a lot of access to the outside world (which the flame and the filler rod are in). A lug has very little edge (shoreline) compared to the internal surface area, resulting in the need to use capillary action a lot more when filling a lugged joint.

So, yes, I agree. Andy