Thanks for all the replies.
Couple of additional pictures so you can see where the antenna is currently located. Just measured, so the console is 48" from the deck to the top of stainless steel grab-rail. The Metz antenna measures 36" in height. It's never given great performance, and I'd expect more traffic when scanning channels. Moving it from the grab-rail (in front of the console) helped, but I'm still not convinced. I thought there might even be disruption because the ICOM receiver is relatively close. I also re-soldered the antenna connections and have checked continuity with a multimeter, so is 100%. The ICOM M411 unit was also new this year.
Looking at the transom, there's probably only one place the light pole can go, which is to the right of the transom support leg. I measured here and reckon I have about 35" of clearance, which is about the same height as the engine cowl, before the garage up-and-over door catches it.
So couple of options, either a detachable light pole, or hinged so it can fold forward. In terms of a suitable height, 6' or so?