I hate PzIVs

[PoorOldSpike]

...SO: HOW THE HELL CAN I BE SEEN BUT BE BLIND TO HIM?..

Probably depended to a large extent on what Difficulty level you were playing at mate, because spotting abilty varies a lot between them. (the Borg or non-Borg spotting thing)
These are the CMx2 Diff levels (Manual page 28)-
IRON
ELITE
WARRIOR
VETERAN
BASIC TRAINING

The Manual seems to recommend Vet level and says-
"VETERAN
Most people familiar with the Combat Mission game system will prefer this setting. It is a fair balance between realism and fun that does not burden the player with unnecessary details or long waiting times.."

Incidentally, you said your tanks couldn't see the 6-pounder but your infantry could.
No sweat, you can still order your tanks to Area Fire into the guns reported position even though they can't see it..:)

But I agree with you that the old CMx1 game engine is better than CMx2, but sadly the CMx1 graphics are 14 years old now and pretty primitive, that's the only reason I switched to CMx2 with its much better graphics.
Ideally, Bfront should have simply kept the old CMx1 engine and given it a makeover with snazzy new graphics.