This is a pure straightline antenna. The peaks are antenna gain for min range reception. The direct feed is for waterfall clutter.
There is nothing in the path between the peaks for this antenna that is not over a horizontal plane.
I include a graph for the 7.5ft to 17.5ft
Since the graph was made with 7.5ft ANT and 13.5 ft ANT, the peak gain is really the Peak gain for 6. 50e0806aeb randas