QFN Standoff (Solder Joint) Height
That's going to be determined by the thickness of the stencil and the opening size, or if no stencil the thickness of the solder paste printed on the board.  I believe it's a warning that too much paste will float the part and then you might not get good joints all around, or maybe the part might be uneven etc.

The only way you could affect it is if you are defining the paste layer yourself then you define the opening and put an assembly note in about stencil thickness.

But really I would say you should leave this to your assembly house to adjust correctly for their process when they order the stencils.  They have to look at all the parts in the board and find a method that will work for all of them, it's part of the magic of being a good assembly house.

Here by the way is a link that talks about it more.  Note that their guideline if a 2-3 mil standoff is "after assembly". Not a you should have a 2-3 mil standoff before assembly...