I've got PUI 68 Deluxe Houndstooth seatcovers and ACI Deluxe Foams. At the base of the seatback foam the distance across is 12 inches for the channel that the hogrings go in to hold the seatcover tails. The base of the back of the seatcover tails that the rings attach to are 11 inches across. Which is correct the 12 inches for the foam or the 11 inches for the seat tails?