Interesting observation John .....my DB6NT based 2.5w 24ghz system with 60cm dish , is currently off the mast .
my garden backs onto MOD land with a line of 50ft , closely spaced chestnut trees about 3m away from mast .
the outlook to the other 3 sides of the qth is similar, but trees are about 25m away .
will put transverter back on mast at 45ft ...see if get similar results to you .
steve G4HTZ JO01JN
apologies for any grammar or punctuation mistakes ....I only got GCSE 3 in 1976 !!