This is the most building error that builders do, countersinking far to deep to nest a dimpeld sheet onto aluminum structure.
Look at this picture:
This is a piece of aluminium angle, drilled and countersunk to accept a sheet aluminium which is dimpled. Then immersed in epoxy, cured, cut and grinded. So that the desaster gets visible ...
From left to right:
1. The aluminium angle is countersunk until a AN426AD-3-X rivet sits flush.
2. Countersunk until a AN426AD-3-X sits 0.01" deeper than flush.
3. 0.018" deeper than flush.
4. 0.02" deeper than flush.
The picture is not perfect, nor the samples are ... but it shows clearly what will happen. Where metal to metal is in contact and where are gaps. The gap between the angle and the sheet material, between the rivets doesent matter at all, but the gap of the two materials inside the countersunk hole and the dimple let me feel unconfortable!
For sure this got measured with a rivet ... which has also its tolerances.
The measurements are done by a caliper ...
Stay strong with Vans instructions, chapter 5 !
as Scott mentioned (he was working many years for Vans Aircraft btw
The clicks may be not the same on all brands of countersunk cages! Test on scrap first.