User blog comment:AbsoluteLuck/In depth analysis of ASW/@comment-24333579-20160401054240/@comment-26247760-20160401124154

Pairing sonars + depth charge have the same multiplier as 3 sonar and 1 Depth charge. So its just best to use whichever has the highest ASW stat once you have one of each.

10 starred modernized sonars does increase in performance. However, once you hit daytime asw cap, it will not increase asw by much. Therefore, its best to aim to reach asw cap and then stop upgrading.