Most imported part to be clean in a skimmer neck?

[Jeto2004]

Here is an question I have been pondering. Got an automatic skin cleaner and it works great in general. However, how it is setup I have either 1/2 inch on top or the bottom not cleaned by the cleaner. So here is my question: Which part of the neck is better to have clean for best performance of the skimmer top or bottom?

 

[Retro Reefer]

Great question.. Just off the top of my head I would say keeping the top of neck clean would be more important. my thinking is you don't want anything blocking the skimmate foam from rising out of the neck and spilling over into collection cup.. It's been my observation that the foam tends to collects near the top of neck before spilling over into cup, anything potentially hampering or blocking that probably isn't a good idea.