How does the unit scaling works in EE2?

I'd like to play around with the unit scaling of the game to see what looks and play the best.

Unit's ddf files define scaling types such as:
kScaleUnit
kScaleVehicle
kScaleMountedUnit
...
And it seems there are a corresponding global parameters to match such as:
g_UnitScale
g_VehilcleScale
g_MountedUnitScale
...

However while testing it felt like the scaling system was broken. I was only able to scale soldiers down, and not vehicles for example, and only when using very low values for g_UnitScale like 0.03 to 0.12
0.5 would not produce any meaningful changes.

DDF files define a scale aswell and for some units like leaders there's a ForceScale attribute. So I assume I could re-scale all type of units that way, but obviously I'd rather not edit more than what I need to tweak the unit size differences.