[in_vino_vomitus]

I don't play SH3, but as has been said, Geometry is geometry. What I've found, playing the German side in OM, is that when you're taking shots with big gyro angles, your target data needs to be pretty much perfect. There's quite a comfortable safety margin in shots taken with a 90 degree approach /zero gyro angle setup. The range is rendered irrelevant for starters, and if your course estimate is out by ten degrees or so, then that needn't matter too much either. It's a very forgiving setup, but as soon as you start shooting sideways, you lose that safety margin. If you want a 90 degree gyro angle shot to hit, then you have to have pretty much 100% accuracy in your target data. Someone with a better head for trigonometry will be able to explain it better than me, but one obvious detail is that if you're aiming at a target abeam, then parallax becomes an issue, because the torpedo is going to be starting its run a hundred or so feet to one side of where you're aiming it from.

Maybe go into the mission editor and set yourself up a 90 degree shot, so that you know your target data is absolutely spot on. if that misses, then you have reason to suspect issues with the game optics, but otherwise it's more likely to be cumulative errors in your course, speed and range estimates.