This is brilliant. I've thought about this problem before since some of my friends face it. Good job Sam.
I tried the demo website as a user and went for the What's my size feature. I choose that I prefer the regular fit but in the recommendation it showed that the recommended size (L) lies closer to the red Tight side on the spectrum. If I choose the larger size, the arrow will go to green side of the spectrum, yet, there is a red (x) on the larger size. I couldn't understand it completely, should I go for tighter recommended L or the not-recommended regular fit XL.
I felt like sharing this. Hope it's useful.
Yousef