First of all you are mislead by the manufacture. It is an off center fed antenna, it is NOT a Windom. A true Windom is a vertical arry with an off center tap on the top hat. The entire array is fed against a ground radial system.
Now that we have determined you were looking at an Off Center Fed antenna, you erect it like you would a dipole.
In other words, what is pictured is an 80 meter OCF. So....on 80 meters it will radiate the same as a standard 80 meter
center fed dipole. Both are 1/2 wave 80 meter antennas fed at two different impedance points along the wire.
If you like inverted vee type antennas, than erect the OCF as an inverted vee. There is no secret formula to mounting an
OCF. For better low angle radiation, mount it as high as you can. If you can not, just erect it in the best way you can.
My OCF80 is mounted at 55 feet as an inverted vee at my primary location. Works great on all bands. I work a lot of DX
with it from 10 to 80 meters. When I set up portable, I put the balun at 30 feet and tie the ends about 4 feet above the
ground. Again, I work lots of DX and it works great.
Here are what the radiation patters look like for numerous OCFs on all bands.http://www.hypowerantenna.com/products/off-center-fed-antenna/off-center-fed-radiation-pattern#80meter
The key to this antenna is, "it is a resonant antenna on numerous bands. " It is not resoant on 15 meters. You are feeding
this antenna at a voltage point on 15 meters and that can damage the balun.