Are these bins Gridfinity 'compliant'?

[ilium007]

The design doc from Zack Freedman shows 1U being 7mm and a base and one unit combined to equal 2U. I would have expected a 3U bin to measure 21mm from base to top but these measure 24.8mm

Where does the extra 3.8mm come from?

I am designing my own Gridfinity trays using this Fusion plugin but also printing other peoples designs and my 3U tray does not match height on other 3U bins I have downloaded and printed.

Confused.