After some investigation, I have established the following:
1) "Classic steel" is the one that is sometimes destructible, depending on the location of the skill assignment relative to the steel area. This is to replicate the bug present in many early Lemmings platforms, and is largely undesirable.
2) Confusingly, "Autosteel" and "Simple Autosteel" options are interpreted differently by SuperLemmini than by NeoLemmix, thus:
[SuperLemmini]{Autosteel} = The steel area fits the steel block
exactly, and is indestructible
[NeoLemmix]{Autosteel} = The steel area fits
only the visible part of the steel block, and is indestructible
[SuperLemmini]{Simple Autosteel} = No function (the steel is completely destructible)
[NeoLemmix]{Simple Autosteel} = The steel area fits the steel block
exactly, and is indestructible
3) I have detailed how each destructive skill interacts with "SuperLemmini-style Autosteel" in
this post. Worth a look if you're interested.
The only thing I don't know is if the resizing of the steel area is exactly fit with the steel block.
Doing this results in the exact same behaviour as enabling "Autosteel" for SuperLemmini levels (as opposed to the NeoLemmix Autosteel behaviour). So, maybe check if Autosteel has been enabled as well?
There are definitely some bugs relating to steel in SuperLemmini, that - upon closer inspection - appear to be exclusive
to SuperLemmini, as opposed to emulation or modelling behaviour.
also I do notice some traps trigger points are too big too in SL. especially those shadow set smasher traps. The lemmings have to be farther away than with the NL same traps.
So I do think there are still issues in SL that are annoying. I just wish Tsyu was online more so we could ask him these questions.
Agreed re: Tsyu.
The shadow traps could have something to do with their position; I've noticed that objects are often offset slightly between LVL and NXLV conversions. In fact, the LVLs of
Oh No! which you extracted are sometimes quite NeoLemmix-unfriendly for this exact reason, and the objects do need to be moved manually to match what's expected. I've needed to do several level updates to
Amiga Lemmings, and I'll likely simply end up using the original NXLVs in the next update for that particular pack.