It all depends on the infantry you are talking about, as well as the period in the war. In most cases you are supposed to rely on other tanks, tank destroyers, aircraft and anti-tank guns to counter enemy armor, not infantry. Heavy artillery can be used to an effect, but again it depends on too many variables to make such a broad statement. On the other hand, the later war infantry units that have no hard attack range mean that they either have to assault, or be assaulted by tanks to destroy them. It is all a matter of looking the numbers.
In a Prokhorovka test I have going on (1943), three Russian guards infantry battalions have been assaulting and pushing back SS PzKw IIIm tanks to good effect, but yes, if I just sat still in the open and let the tanks shoot me then I would not be about to counter. Anyway, these ranges are directly taken from McNamara's own numbers. The infantry units that have an "offensive" AT rating usually have a lower hard attack value than the ones that don't (to encourage close assault). Not that these numbers are the gospel, but they work well enough for me if you know the strengths and weaknesses of everything. Try backing up your infantry with some dug in AT guns is about all I can really say. You may find yourself in cases of extreme overmatch. In those cases, you or your opponent has to rush the counter to that overmatch to the area. Think rock, paper, scissors. ;)
As for the early war years, there isn't much of a choice. I think all infantry have 0 hard attack range since any AT capability they had was extremely limited. Then again, the early war tanks aren't that difficult to kill with air, artillery and anti-aircraft guns either.
Quote:If TD defense is based on having accompanying infantry in some cases then at least they should be able to fire at them.
Not necessarily. The McN numbers are calculated off of four values, defense, front armor, side armor and rear armor. The defensive effect that "tankos" provide is not a huge amount -- not so much that you can say that you should be able to target the tankos to kill a TD. That said, you are free to change the values to whatever you like of course.