Those black collars will never flush up to the scupper openings on the Pro Angler as the shape of the collars and the contour of the bottom does not allow that. At least that's my experience with a 2012 PA14 and a 2013 PA14 and 2 Heavy Duty carts. I have found that by using 2 tennis balls drilled out and put on the shafts without the collars, I get enough clearance off the wheels and the end of the cart sticks through fine to use the retainer pin.
But I do not pull my PAs on the carts fully loaded very often. I use the carts mainly for pulling the PAs in the driveway for cleaning after an outing. Some folks have suggested using a small piece of PVC below the collars. I might try that in the future.
Just my 2 cents. BTW...congratulations on the PA purchase!!
I hope you like it as much as I do!