How are heart rate zones calculated on my Apple Watch?

I was checking how Apple came to the heart rate ranges it is showing for my target heart rate zones in the Workout app. In the explanation it says that these are calculated from your max heart rate (MHR) which is calculated with the formula 220-Age. In my case my MHR is 167bpm so the min and max threshholds for the zones should be calculated as 50%*167, 60%*167, 70%*167 etc… But when I backwards calculate from the zones that my watch is showing this is not at all the case! If I devide each lower and upper heart rate by the same percentages it actually gives a different MHR each time, ranging from 177 to 207. Where 207 would be my MHR based on a upper 60% treshold in zone 1 (my app shows zone 1 as <124bpm) ? But the lower treshold of my zone 5 says >159bpm at 90% which would equal an MHR of 177. This makes no sense. It look like the app is stretching the upper end of the zones and pushing the lower ends up (my zone one based on my MHR should be <100 for instance). I cannot find any explanation online to why Apple is showing different ranges for each zone as what is typically used in the calculations that experts provide. Does someone here have a suggestion?

[Re-Titled by Moderator]