This has more to do with firing at the base sector or at set up OKW trucks. You know exactly where you need to shoot in the FOW to hit the mark, no recon required.
You say it is easy for Stuka dive bomb to do it with scouting, so why can't B4 do it?
Well, it can, but what for? Shooting 90 muni in random, when you can spend 80 more and see targets clearly? You also have to calculate where to strike with that P.S. for to get result, and for that you also need vision.
Would you drop Stuka Bomb (if it could be possible) in fog, without knowing where is the enemy? I think no.
And yea - shooting at HQs is not best way of using B-4. I prefer to use it for to destroy heavy and superheavy tanks, like KT or JT. And sometimes infantry, but it requiers too much luck from you. At least, KT/JT it can hited sometimes, so big those tanks are.