I completed FTP/MAP Builds: 2 Sets 4 x 4 as part of my MTB Marathon plan yesterday.
This workout consists of 4min efforts, 3 min @ FTP ended with 1 min @ 90% of MAP.
The 3 min @ FTP: 7.5 / 10 RPE in Z4 HR zone.
The 1 min @ 90% of MAP: 9 / 10 RPE in Z3 HR zone.
HR zones of those efforts should be the other way around.
It is even stated in the description part which, BTW, has yet another error (effort duration):
Paced correctly, your heart rate should essentially be increasing for the entire 6-minutes, as it will be setting into LTHR right as you up the power output.