Classic Car Clamp On 105mm Polished Stainless Steel, Round Exterior Mirror - For Minis - 950M

I am fitting the mirror bracket to the seam moulding on a Mini so that's OK the problem is the stud ball fixing and the plate with the three screw that holds the stud ball in position on the back of the mirror, there is a 3mm cap approx as you cannot tighten the plate down so it sits flush with the back of the mirror without a spacer, this means the three screw plate can move around on the stud ball at the correct tension so you can adjust the mirror or not if you over tighten. What’s wrong? The outer circumference of the three screw plate needs to make contact with a hard surface so when your tightening the three screws pressure is put on the out circumference of the plate to secure then the final tension so the ball so you can adjust the mirror which holds its position, it’s a shame it does not come with a spacer so would need to make one if I decide to keep it, anyone else with the same problem?