Or instead, units cannot target units that are behind a larger unit. That way MGs cannot shoot “through” a tank or AT guns targeting a tank that is behind another tank. This would open up lots of options for combined arms tank play and the use of rifle grenades, mortars and other forms of light indirect fire to counter it by targeting units behind taller units.
Depending on how Relic calculates vision, having different height vehicles may be troublesome to code. However, they already have sight blockers. Having TANKS be "MOVING SIGHT BLOCKERS" may be very simple to code. They already have the code. Copy-Pasta and they are done.
This would be very interesting to play in 4v4. It would nearly nullify MGs/bunker spam. Historians may argue you could shoot between the tracks etc. So I guess the green cover mechanic is more historically accurate?
You could also then push garbage vehicles in front to break through lines and protect your expensive vehicles.