With a Quad Fin Setup, it is my understanding that if the fins are of two different sizes, the larger fin should be placed nearest the rail. Has anyone tried them the other way - with the smaller fin near the rail ? What is the effect or difference. Thanks in advance.
It is called a Twinzer setup, but it wont work with the standard quad boxes position.
Just exchanging the fin position on a standard quad setup will make the board too stiff.
On a quad/thruster, you use the front fins as your main "airplane wings" top provide all the lift/hold in turns, and the rear(s) act as stabilizers. And as SUPs are already much stiffer (bigger/longer/heavier) than shortboards, you need even smaller rears than the ones used on shortboards to compensate.
Plus your quad rears have probably a 80/20 or 70/30 profile, and thus provide even less lift/hold than true side fins.
Twinzers work differently, the main wing is the rear fin, and the front fin is there just to redirect the flow onto the rear fin so that it works better. So the position of the fins are critical and very different from a standard quad setup.