Yes, very interesting...

One thing that I think could be better teased out though is: absolute duration vs relative duration

That is: While keeping high intensity minutes fairly constant, did they simply shift the remaining minutes from moderate to easy (with the total minutes staying constant)? Or, did they shift the minutes from moderate to easy AND add additional easy minutes (thus increasing the total minutes of training)?

The studies were maybe a little inconsistent in that -- but my sense is that, generally, they increased the total training time to increase the total minutes below VT1. That is, that there was BOTH a change in percentages (from the middle levels out to either side) as well as a change in total training time with most of the increased time in the low intensity levels...