[PlasmaKrab]

OK, I get the idea.
Look at it closely and you'll notice that these missiles have a basic AP penetration value, not HEAT. In other words, they are KE missiles...
No need for a tandem warhead then, right?
Look up the US CKEM and LOSAT, which work the same way.
I've tested this modelization of KEMs, and the PA value doesn't draw down with range, the resistance to basic ERA is rather good, and the AP values takes on the steel armor value of the target without problem.
Only issue I'm having is that since these missiles are class-13 standard ATGMs as you noted, and with rather lower penetration values than HEAT weapons, the cost is artificially low.