OK, That is clear enough. With the meter at three meters from fuselage centerline, a vibrating wingtip will easily spoil the measurement because of it's very closeness to the meter with large models. They do seem to allow for the hard ground by adding about 3 dB though. 94 dB over macadam equals about 91 over grass (not very short, but normally cut).
I like our industry standard distance of 7 meters better.
I wonder how your salt dampens the noise. I imagine it not being as closed a surface as macadam?