Taking the limitations into account this would be a way to go.
A high gain Omnidirectional antenna would be your best bet as this provides more coverage in the horizontal direction as compared to the vertical.
If the signal is to be focussed downwards towards the dig site from the control room, then a high gain directional antenna would be your choice.
I would suggest contact your sales rep and have a test run with the internal antennas and without them.
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