How to fire on HQ-Units if you can´t identify them ? Especially if the Fog is on "extreme" it would be rather difficult.
You should shoot primary on Tankcommanders. So the sniper becomes a very important "tankbattle-support"-unit: While the Commanders, you`ve shot at, are "button up", they can see only half of their normal potential...or even less, so you can get your tanks or guns in Position and have one or even more "freeshots" before the enemy can react. If you have an experienced sniper, you can even kill the commander at "long range" with a good chance, so the rest of the tank crew is mostly shocked, what will makes the tank "out of order" for a few seconds - an easy target.
Some tanks you can even destroy or at least gwt to "abandoned". For example the Marder-Series, which have an open back. One shot in there and the crew is at least "panic".
If there are no enemy tanks on the whole map, you could concentrate your snipers on guns in pure cover (especially from behind or the sides), mortar-teams, arti-spotters and other vehicles. If there is really nothing else to shoot at, then you could attack normal infantry, when they pass open grond (for better results).
10 Rounds for a sniper is not historically but i think the devs want to simulate, that a sniper should shoot on "special" targets, like commanders and so on. What would you do if you have 60 rounds to go ? Right - you would shoot at every single infantrygroup that pass by.
But with just 10 Rounds you must think of, which target you want to shoot at. A little Advise: Sometimes it is better to give a Sniper a Cover Arc, to prevent him from shooting at Infantry, that moves along.
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Sorry for my bad english.