a decent antenna: like this one - $32USD...
Actually that's a pretty crappy aerial, not a 'decent' one at all - more a toy than a proper aerial, and will have VERY low gain.
Well, I guess it all depends on how you define "decent".
Looking at CBBs picture, there appears to be a long folded dipole in the plane of the (parabolic) reflector.
This dipole appears to be intended for VHF.
There are three "bow tie" elements of different sizes for UHF , how they are connected is not clear (to me), my best guess is that they are all connected in parallel with the VHF folded dipole.
The differing sizes of the UHF elements implies that this antenna is intended to be a wide band, low gain, one size fits all type of thing.
The reflector, for all its elements, is unlikely to have any effect at VHF, and a small effect at UHF.
We're "line-of-sight" with the tower.
Well, there you go!
Likely a good signal strength area, a low gain antenna is fit for purpose. End of problem.
I spent 46+ years in the TV trade, including fitting aerials occasionally
In Derbyshire no doubt.
For those unfamiliar with the geography of England, Derbyshire is all hills and valleys, most people live in the valleys where line of site is at best not very far. So you end up with two problems, a weak signal and numerous reflections off the various hills.
The antenna of choice for such situations is a long Yagi having 20 or more elements. Lots of gain to boost the wanted signal and a narrow beamwidth to attenuate the reflected signals.
JimB