Thanks @burble, for following up on this and posting your findings.
I'm experimenting with a couple of other arrangements at the moment, but it looks as if a USB antenna may also be worth considering.
I'm trying out a quick, simple, cheap and cheerful option at the moment - a TP-Link WA854RE range-extender/repeater. Doesn't make a massive difference, but choosing the right location between router and garden room does seem to extend the range and gives a stronger signal in the latter location, which is good.
Thanks to another kind forum member I also have the opportunity to try a Devolo Powerline arrangement - which I plan to set up in the next week or two just to see how it performs.
And then maybe I'll go looking for a USB antenna, especially if I feel the need for a better signal further away from the house....
Edited by br1anstorm (Wed 12-Mar-25 18:27:51)