To change the max depth you need to alter the ZON file.
Editing the cfg will not work.
In the ZON file there is an entry called CRASHDEPTH.
Despite what you may think, this is actually controlling the max depth for the sub.
I know this is a counter intuitive connection.
Please see screenshot for proof.
This is from an SH4 boat, I have been playing with the crush depths of my porpoise this morning.
The SH5 ZON files have the same entries.
Again. Editing the cfg file entries will not change the boats max depth characteristc.