The problem here is that infantrymen are only issued AT weapons to make them feel better.
Your average Joe with a LAW, M136, or SRAW isn't going to scratch a tank unless he can catch it in a close-range ambush with a side or rear shot. OFP can't really simulate ambushes and in fact the AT weapons in the game are rediculously overpowered.
A guy I know was a Dragon gunner back in the mid-80s and he said the LAW was so worthless against armor that they were trained to use it against bunkers, jeeps, and people.
American infantrymen carry the M136 or SRAW and Rangers carry the Carl Gustav - none of them are powerful enough to take out an MBT. While I'm on the topic, I should tell you that the real Carl Gustav isn't nearly as big or powerful as OFP makes it.
ATGMs are a different story - the Javelin can blast a T-72 into rubble (I've seen viedo), but not every infantry team has one because of their size and cost.
Basically, infantrymen don't fight tanks unless they can set up an ambush. OFP gives a huge boost to the AT weapons so that you can take them out, but in real life if you see a tank, you either hide, run like hell, or hope there's a gunship or friendly tank nearby.
So, how can you make it more realistic?
You'd have to drop the power of all the AT weapons in the game. When you've done that, you need to drop the engagement range of AT soldiers A LOT and somehow make them only attack the sides or rear of tanks. Finally, you need to make all tanks in the game practically blind when they're buttoned up (as they are in real life).
O Neil is right - if they spot a tank they should get down, find cover, and wait for the tank to get in close before popping their AT weapons.