I think the trick is to make the same kind of run each time. If you use the bottom of your guns site you must make the same run each time. If you come in at a 45 degree angle and miss short with the bottom of the site, then coming in at 85 degrees with the bottom of the site will come in long.
Ideally 45 degrees is good. At 45, looking out the side window your horizon line is from corner to corner so its easy to see if your on the right angle. Depending on the site you use the firering position might be lower than the bottom of the site. Go to the TA, enable the LCS and see where the cross hairs line up in your site at 45 degree dive angle. Last is going to be range, and this is just practice. At the 45 degree angle, there will be some drop due to gravity. The longer the range, the more the drop.
Lusche covered the IL2 pretty well.