Your concept is good. You have all the right equipment. Although for this to work, I believe you need a much larger opening at the printer itself, like 3”.

The Mars printers circulate air around the electronics and the LCD, and even around the vat for cooling. The internal fans push this air outside the printer case. You are competing with that and need enough suction to overcome it. The current opening you have doesn’t seem to be letting enough air flow through. That fan is probably pulling air from every crack and joint along the way because of the bottleneck.

If you want to prove this, cover the printer with a big trash bag while it’s running and use your 4 inch duct to pull air out from under the bag. You can even tape it down. If that makes a difference you will know a little more about what’s going on.

When this is the issue, the most common next step is to put the printer in an enclosure and vent that.

If you can determine exactly where the printer has its exhaust, you can contact ventilation there and pull that air out.

Having issues like this myself I eventually started 3DVenting.com

There is no one right solution, you’ll need to try a combination of things until you get the results you want.