Nice Steve... Some of these manifolds are really good, others not that good, in order to ensure perfect exhaust pressure relief using a external wastegate, there should be a pipe/pipes that is able to collect as much of the exhaust gases from EACH primary pipe from each cylinder. The angle of this pipe/pipes should be as close as possible to go in line with the flow from the primary pipes from which you want to release exhaust pressure from.
The drawback with doing a solution like this is that it steals a lot of the flow even when pressure should not be released from the manifold. Therefore, its more common to perform solutions as seen on many of the manifolds in the picture, 90+-10 degrees from the appreciated flow angle.