I'm going to clear up a few thing that some people get wrong regarding shooting at vehicles. The first issue is which armour value you're firing at. Some people are under the impression that you use a imaginary line 45 degrees from the corner of the vehicle. That's not correct. When determining which armour value you will be firing at you run a line from corner to corner on the vehicle being shot. This means that longer vehicles like chimeras are easier to shoot in the side armour than say, a dreadnought.
Some people also seem to be under the impression that when determining if a vehicle gets cover, 50% of the vehicle needs to be obscured. This is not true. Only 50% of the armour value you are shooting at needs to be in cover, so is entirely reasonably for a vehicle to be over 50% visible and still get a cover save.