What difference does the shape of the boiler lid make?

[wombatvvv]

I was just watching a YouTube video on making a pot still. The guy was using a pressure cooker with a flat lid. He mentioned because the lid was not domed, it was only suitable for distilling basic sugar wash and the like. Seriously? What difference does the shape of the lid make?

What about the thickness of the pipe coming out of the lid? Would it be best to use a 2" copper pipe connected to a mixing bowl for a lid? Or does the pipe thickness not matter? I ask only because I've been watching some doccos on professional distilling, and noted that their pot stills are basically huge cones. The only way I could think to emulate that is with a very thick pipe coming out of a mixing bowl.

Not that I'm planning on distilling high quality single malt. lol. I'm just curious. I may as well build the best thing I can.

As always, sorry if my questions are stupid. I'm too much of a newb to know what's stupid and what's not. Or even what to search for in order to find out.

Much appreciation for your time.

Vic.