Looking for a clear explanation...

[Panama]

As far as I can tell Penetration is the thickness of the armor an AP round will penetrate at POINT BLANK RANGE. It would be nice to have penetration values at different ranges but those are not listed. Just point blank. I guess that must be one hex or less. HEAT rounds don't matter. Same at any range. APCR or Sabot rounds are usually more effective at shorter ranges than straight AP because they don't shoot as far.

Range is how far it shoots. Sometimes given in minimum/maximum value.

Warhead is how large the shell is. Kind of like how big of a bang it makes. Bigger is better.

Kill is lethality probably. Bigger is better. It's a High Explosive value I think. Not for penetration although a 152mm HE shell fired with direct fire at any tank will cause extreme suffering to the occupants.

Firing AP at a small tank can sometimes be frustrating simply because the round passes directly through the entire tank. Especially larger rounds. A smaller round might get through the front and then rattle around inside for a bit. Ouch.

Your infantry should be able to handle a light tank one would think. In any event, this is my take on it and it's probably fairly true in most wargames that are somewhat realistic.