Look at the lnb that was attached to the reflector on the sat dish, then look at the bow tie.
The bow tie is soooo much larger that the orifice for the lnb that most of it will lie totally out of the focal point of the dish.
It may block some radiation from the rear, but satellite dishes are too small and the focal point is too small for it to work efficiently on UHF TV reception.
Look at the old Channel Master parabolic antennas, they were about 6 ft in diameter and the reflector was about 3-4 ft behind the bow tie, and these worked because that was what they were designed for.
A small 18" reflector will have a small effective gain.
Look at the standard reflector for bow-tie type antennas they are maybe 3-4 inches behind the bow tie and that works, too.
For best reception get and antenna and use it for the purpose for which it was designed.