Seperator inlet size

[bagger don]

This is my first post here but I have read quite a bit of valuable info he over the last couple of months. I have already built The Thien separator with silver can under my Delta 50-760. Thanks Phil for sharing it with your fellow woodworkers. I am currently running a 4" S&D elbow for the inlet and in process of making my own blast gates for a 6" main line and dual 4" sections to my 5 machines. I have a 15' max run and will only have one gate open at a time. Should I make a new lid with a 6" elbow intake or keep my current 4" and use an adapter.

Thanks in advance for any assistance,
Don