I want to match a 50-ohm coax feed wire to a 40-meter NVIS half-wave dipole. NVIS antenna examples I've found are usually based on a regular dipole (72 ohms in free air). However the impedance drops by a factor of four (to 12 ohms) when it is lowered to 7 feet (https://www.w9xt.com/page_radio_gadgets_nvis_antenna.html). (Note: the author's numbers seem not to correlate with his factor, but at any rate the impedance drops very low).
Just for reference, a folded dipole in free air is between 200 and 300 ohms (https://www.w8ji.com/folded_dipole.htm). Therefore, its impedance would drop by a factor of four to 50-75 ohms, making it closely match 50 ohm coax.
My idea was for a regular dipole (not a folded dipole) and use a 4:1 balun to raise the antenna impedance by a factor of four from 12.5 ohms to 50) to match the coax and transmitter impedance.
Problem: Maybe some baluns are not designed to be reversed because the side designed to be high impedance balanced antenna would then be on the unbalanced coax, and vice versa with the low impedance side. Furthermore, transferring power the side driving the low impedance antenna might draw more current than the balun wire was designed for.
I have not found answers in any Radio Amateur's Handbook (I have six ranging from 1956 through 2012), or on the Internet.
So what is the proper way to match 50-ohm unbalanced coax to 12.5 ohm balanced dipole?