We never played it that way. As the Tank blocked LOS and provide cover ... and in turn would get hit by the APers rounds meant for the Infantry. And would have no real appreciable effect on the Infantry. But you can play as you like. But with a lot of units on the board you might be adding more detail than needed. And the question again is what is shooting at the infantry, AT or APers.
As far as how much cover, is again ... based on LOS ... the direction the fire is coming from. What can the firing unit see of the Infantry ? If can only see 50% or less of the target/Infantry ... the Infantry gets cover.
And yes in modern warfare all Infantry has AT weapons.
My Plt in the 101 ABN, each 11 man Squad , an 1 Dragon M47 MAW was in one of the Fire Tms
[Squads had 2 Fire Tms of 5 men each and then the SL made 11. ]
[ 3 Squads per Plt + 3-4 man Plt HQ/CP]
Each 5 man Fire Tm had an M203 GL with could fire HEDP rounds with could penetrate 2 ins/50mm of armor. Along with the M47. And the others in the Fire Tm could be issued M72 LAWs.
The other 5 man Fire Tm was the same except for the M47 MAW was replaced with an M60 MG.
So yes, all Infantrymen have AT weapons ... But you normally would Not fire the M47 or M72s at Infantry unless they are in a bunker, building etc. ...
But again ... play the game as you wish ...