That's correct, at the 1.15 mark. I will give it a go from that point.The antenna starts at the point that the center conductor is no longer surrounded by any sort of shielding. It's not really clear to me where that is, in the picture you posted, but I would guess it to be at the 1.15" mark.
Probably. That doesn't look at all like a mount that was designed for 800 MHz use.That's correct, at the 1.15 mark. I will give it a go from that point.
If the point that the center conductor starts were closer to the roof would it be better?
I have another one that is lower. I'll save this for something else.Probably. That doesn't look at all like a mount that was designed for 800 MHz use.