Feeding at the top will result in Horizontal Polarization and with the apex
only at 70 feet, not desirable results for DX/Contesting. In fact, I would
argue that you would be better off with the inverted vee that you have
rather than to do that.
The proper vertical feedpoint is actually 1/4 wavelength down the sloping
side wire, not at the corner. The corner actually produces a combination of
vertical and horizontal radiation but because the vertical is more than the
horizontal, and it is bloody convenient, it is often fed there. Maybe this
true feedpoint will help you out.
If not, post this on "towertalk" and you will get lots of helpful ideas.
73 and GL,
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