OK - didn't spot the new option, I was looking in Developer Options! I've changed to 200 and I will see what happens with the BT browsing.
When BT browsing I see Now Playing(BT) node - 20 previous and 20 next doesn't seem to be as many as I could see, I will double check this though, and it didn't seem to be scrolled to the currently playing track on BT browsing - again, I will double check when I am not driving
If you have fixed the Android Auto browsing issues I might go back to that anyway, the only reason I was using BT was the issue with the lists in Android Auto. I'll experiment with different list lengths.
I have one question about Android Auto though - which device converts the audio - the phone or the Head Unit? I have always found the volume level via Android Auto to be quite a bit lower than all the other sources on my HU and no way to adjust it, so have to crank the volume up quite a bit ...... I know this is probably a HU issue, but it has been the same across different phones on different Android versions in to different OEM Head Units in VAG group cars (2 x Skoda Columbus HU, which is basically a VW Discover Pro HU)
Thanks for the detailed and prompt response