Your Camlock fasteners do not provide any means of adjustment to the fastener itself. You can reduce the thickness of the overall stack up of parts by removing material (sanding/filing etc.) or adding shims if they are loose. You can also purchase different lengths of Camlock fasteners or receptacles, but my guess is the size you have installed are as close as you’re going to get. The Skybolt brand fasteners do have provisions for adjustment, in fact they make a kit specifically for the Vans oil door. Your options are, remove material by filing/ sanding to reduce the overall stack up, or remove the Camlock style fasteners and replace them with Skybolt fasteners and receptacles.