Anytime you are mounting pads to a machine you always want to ensure that you select the largest plate available that will fit on the Velcro of the pad. Reason being is that you get more support across the pad and will transfer even distribution through the pad to the paint.
If you are using a 4" plate on a 5.5" CCS pad, it has a 5" Velcro mounting material on the backside of the pad and a you are losing 1/2" plate support around the circumference of the pad. Sure you can use that combination but it will not be very effective. You are much better of with the larger 4 3/8" plate as this will give the necessary support.
I posted this in another thread concerning questions on pad/plate sizes on the Flex 3401.
Below are pictures from a pair of LC 6.5" pads. On the left is the standard 6.5" flat pad. On the right is the 6.5" Hybrid pad.
Notice the bevel and how it shrinks down to a 5.5" Velcro material.
Here is the proper larger 6" plate from the LC plate system attached. See how the plate supports the pad completely?
Here is the standard 5.5" Flex plate mounted to the 6.5" Hybrid pad. This is a perfect match.
Side by side comparison shots
Hope this helps.
