I have been looking at how best to represent forces in 3mm/1:600 for 1940 battles, with particular reference to using the “Portable Wargame” rules.
I am using battle boards with a 1”/25mm grid, but my idea is that a game “grid area” will be 2×2 of the smaller squares. I have been working on re-basing my 3mm models on transparent <1mm thick plastic, using 1 base per strength point. But for ease of play I am also creating multiple bases.
Thus, awaiting careful (re)painting, avoiding the clear plastic, I now have most of the French units for my next battle. I need more infantry to complete the full duplication.
Because of the size of these models, to identify them I intend to put a spot of paint representing the appropriate nationality (e.g. blue for French) underneath the plastic base beneath one of the metal bases. Further ID may be considered, but I think by careful storage and documentation, accompanied by occasional magnification, I can work out what is what!
Mostly unpainted as yet, here is a representative appearance on the game board, with a unit of 2 x 75mm guns, a unit of 3 x S35 tanks, 2 more 75mm guns on the road, 2 units of 16 infantry and one unit of 16 infantry in 4 sub-units, enabling the farm to be shown as occupied.

Each sub-unit (4 men or 1 gun or 1 vehicle) is 1 Strength Point in the rules.