Hmmm...
- worse performance?... Let me make certain we hadn't borked the links for the radar devices... In the meantime, the SV is the "elite" air search, while the ST is the periscope radar. There should be no rotating, unless you do it yourself. CapnScurvy "fixed" that quite a while ago. If the game would only cooperate with conning tower upgrades, all (almost all) would be well in the mod...
- if the ST is in fact "active", its range is much shorter than either SJ or SJ-I, and that might be the issue. Be certain you have lowered your Observation Periscope when it is not needed. If doing a periscope patrol, use the Attack Scope for that... The game can only do one sensor at a time, and ST has the priority when it is applied... which is why we changed the config for the next release...