I’m building a miter saw hood that will be ducted at the bottom with a 5” pipe into a 6x5x3 wye with a flexible 3” duct to the blade guard.

I can run the 5” duct straight into the bottom of the box and have a 5” round hole at the bottom. I can fix a 4”x10” HVAC boot to the bottom that transitions to a 5” duct leaving a 4”x10” rectangle at the bottom.

The labor is a wash. The boot costs $15 which, in the scheme of things, is also a wash.

Objectively, is one option more efficient than the other? What difference in extraction would there be, if any?