To my knowledge, there are no "special" settings. Nor does a green skin do anything more than help you survive by remaining unseen (highly recommended, considering the manueverability of a tank) (stay away from the bright orange default skin, BTW)
One hit kills will happen...good angles, good range and good luck = poof goes the Tiger. If you know the six weak spots to shoot for, set up properly, get a good angle, and hold fire until ready...you'll eat a lot of Tiger Perkies for breakfast.
I''ll tell you how I kill Tigers: Never, ever in open field combat. Do not square off nose to nose. If he starts shootin at you, and has any kind of aim...it's time to scoot to a new position. I'll either a) look for a flanking approach from range, or b) lay in ambush along a favorite travel route, usually on a reverse angle, to make myself very hard to locate. Patience will be key.
Also, if you find yourself a good spot, don't shoot every target at the same relative position. You'll be found. Toy with 'em a bit...let 'em pass by the spot you blasted 'em last time and they'll think they got away. THAT's when you ventilate 'em for maximum customer satisfaction!
Best of Luck!