My suggestion
is that you need a good counterpoise...... Maybe buy a sheet of
corrugated tin from Home Depot, mount the connector in the middle,
with the MFJ on one side and the antenna wire on the other.... You'll
find, I am certain, that your readings will be more consistent.....

This is not a bad ground plane for 2 meters --- I have used one
with good results......
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Alternatively you could use a ground plane of chicken wire mesh ,a bit
easier to handle than a sheet of metal.

Frank GM0CSZ / KN6WH