Very interesting. I have yet to use DPP even though I have shot tons of Canon so did not know this. The result you get adding +40M as a preset is different from using a uniform color addition with the slider tool per your comment above? This little project was my first time doing this but looks like something to keep in mind for future UW color correction. My biggest issue, however, is stained water which I find very challenging to fix in a satisfactory way.
BTW I noticed that even within the normal slider range there can be some nasty artifacts, particularly with clarity.
Yes. The solution is to make a profile with a higher Tint starting point. This one was called 40T - as it adds an extra 40 units of Tint before you start using the Lightroom controls.
String’s problem is that Canon cameras in particular can add more tint in camera (more than +150) than you can in Lightroom (limited to +150). DPP supports this in the Canon RAW file. Lightroom does not. It is why I always tell Canon shooters to use RAW + JPG when shooting filters. Or use this work around.
You can also achieve a similar affect with the sliders in the Camera Calibration module - but I find them fiddly to use. The Custom profile solution is one click simple and it s stored in Lightroom for future use. The profiles are Camera specific.