Hi Simon,
It seems to me that you need an antenna that:-
a) is as far away from your TX antennas as possible
b) is small enough to fit in space available
c) is not blocked by your house or pattern affected by the slope
d) has some directivity and covers a reasonable bandwidth
Someone on the group suggested a mini diamond loop and this seems to fit most of the criteria in that it is small enough to mount anywhere and has reaonable directivity and f/b. It could be relay reversed or rotated for more than just one direction.
https://ok1rr.com/antennas/the-w2pm-mini-diamond-receiving-flag/
You would need a high gain low noise preamp. of course)
I was going to suggest a single support DHDL but it would mean installing it down your garden and even a small one takes 50ft or so.
(I used one for years and with 10dB RDF it was nearly as good as my 550/600ft beverages).
The same applies to a mini-4sq..
The Waller Flag is an excellent antenna and is one of the few if any loops that compares in either vert or horiz form in RDF (near 12dB) to a long beverage but down the garden may not be suitable for your location in its vertically polarised form for reasons you have given. N4IS recommends the HWF to be quite high, so in effect needs a large tower .
I wish I had your low noise location!
73
John
