Hi guys,
To get a rough idea.... attached is a center-fed 5/8 wave antenna at various heights (this is not an exact copy of the 5/8 wave gainmaster) so most likley real performance should be slightly down to what is provided. I think i have a model of the Gainmaster around somewhere, maybe on my other computer.
The main thing would be: As it is a center-fed antenna the overall performance at various heigths isnt that bad at all !
In regards to the astroplane when both are around 50 feet they will have a similair pattern but the astroplane will be just down in gain with 0,5dB or so.
I however can imagine real live results can provide larger differences as the mast is a hugh part of the astroplane to function as an antenna.
Kind regards, Henry