Input Gain Again - any RME UFX II users here?

Hi all!
New Neural user here - loving the Morgans…
So…been down this rabbit hole on input gain.

From RME Admin:
Setting the INST option gives you a max input level of +21 dBu, @ 8 dB gain! So to get +13 dBu as max input level you need +16 dB gain.

So, the maths is sound, however playing my guitars into the Instrument input, with my gain set to +16 on the RME UFX II, I’m only getting a peak dBFS level into logic (also on the RME channel) of around -25dBFS. That seems VERY low. It sounds good, but the waveform in Logic is so small even zoomed its hard to see. It seems excessively low.

If I set my input gain on the RME to around 25 to 27, the dBFS scale in Logic etc is averaging around -13 to -15, which seems ideal and sounds great.

What am I missing here?

Also a comment on a Youtube thread where we were discussing this:
From @ampspedalspickups
I checked the manual and yeah those numbers seem right. Guess there’s a few ways you can balance things. I think +12dbu seems to be a bit of a sweet spot for amp sims so you could just take you interface levels to match +12dbu. In theory to go from +21dbu to +12dbu you need to add 9db of gain. If yours starts on 8 then add 9, if it starts on 0 add 9… either way just add 9db of gain from the lowest available value and that will get you to +12dbu
From there you’ll perfectly match neuraldsp and you can adjust inside the amp sim for other ones, wouldn’t bother touch the gain on the interface again, just know it’s at +12dbu

Cheers…