I had EXACTLY this problem when I cranked up the realism for the first time a few weeks ago (now I'm a convert). Sailor Steve has explained speed and AOB, and to be honest if you're shooting from the right range (less than 1,000m) you can be as much as 45 degrees out on AOB and 50% out on the speed and still hit.
Check out
this thread , lots of helpful Subsimers suggested a gread mod to me which is a bit more realistic and easier to use. Worth a look.