I contacted a friend who has a SteppIr vertical, and asked about what
grounding he used on his installation.  Here is what he had to say:

 

My StepIR Vertical is a 6 thru 40M version with about 10 square feet of
brass screen under same.  I added about 30 square feet of Chicken wire in
2012 when the lawn was refurbished.  This additional wire did not seem to
have any noticeable effect or measurable performance differences.  The wire
mesh is under the surface about 2 inches.

 

He told me that his vertical performs very well.

 

HTH

 

Alan/KD7GC