CapnScurvy did a LOT of work on his
Optical Targeting Correction (OTC) mod to get the FOV and magnifications correct on the US boats, but I do not recall how much work he did for the German boats... you could also check with jimimadrid and maybe he could add the German boats to his recent work with the periscopes and TBT for the US boats, if he hadn't done that yet also...