Hitting into a net outdoors distances WAY off

I have a backyard set up hitting into a net.  I have tried everything like testing different distances between the garmin and the ball and the net.  Also making sure the bottom of the tripod is even with the bottom of the ball. I am running the latest firmware 4.3.0.

The distances are WAY off.  I generally hit a 7 iron around 145, at times this device is telling me it carrying less than 100 yards, but it is almost always 30-40 yards short.

I have a 3 hybrid that I generally hit around 180-185.  This unit is telling me its carrying 110?

I have googled and read this exact same result on many forums here, going back over a year.  I'd appreciate some feedback from other forum users - does this thing just not work hitting into a net?  If so I'd rather know sooner and sell this thing on ebay and buy something else that works.

Any feedback appreicated.