VIIC, in FOTRSU, enemy lookouts are much sharper than stock lookouts. You're saying they won't shoot unless you're above 33', at which point your entire conning tower is above water and your deck is about a foot below the water.
Long before you can get to that level you should be dead. Something is wrong with your game installation and you probably need to completely reinstall SH4UBM to get back to a certified stock installation. That's very easy to do with Steam. Just remove local content and then reinstall from the Steam menu.
Then reinstall JSGME, Large Address Aware (don't even THINK of running FOTRSU without that), and FOTRSU. Then you'll be wondering how to survive the Japanese shooting at your sub so accurately!
