The calibration to an it-8 target is the problem. You need a target for the specific film type you are trying to scan. A Kodak ASA 50 calibration target will only screw you up a little if you are scanning Fuji ASA 50, but when it comes to cine film, you absolutely need to know, and cater for the stock response you are working with.
Using the incorrect colour target, does as you mention, adjust the internl scanner processing, and almost ensures the colour is off.
The film response curves are radically different on feature film stocks to print stocks, and IB is its own thing again, the colour, particularly outside the mid-tones will be skewed. The DMin and DMax is wildly off, as are the response curves compared to a say Fuji Provia 100F it8 target.

If you are viewing the prints projected with the correct light source, at the correct FL on a screen in a darkened room, and matching to what you see, then I agree, you can adjust the scan as best as you can to match what you are seeing on the projected print. If you are looking at the film with a light box surrounded by ambient light, then the colour perception is going to be way off.
Colour is a slippery beast.
Of course the software used to view the results and monitor calibration is another issue, but I’m sure you are running calibrated monitors and software.
It is amazing that even different browsers on the same calibrated PC will give different looking images on OT.COM, sometimes radically so, I’ve gone to comment on someone’s colour corrections in the forums a few times, only to realise that viewing images inside a browser on a forum is completely different to how their images look on their computer.

I love the work you are doing, but when downloading the images, and watching the IB prints here, the colour looks quite different.