I did another brain tree G5 run yesterday, I chose a nice big crater on the daylight side and crossed my fingers. Found some scattered trees and a couple of large forests, 100% polyporous.
I took off glumly, but once in SC I decided not to learn from experience and instead targetted another area on the daylight side (gentle hills iirc). Found a huuuuuge forest, which had all types - I filled my bins. So this was in the same active session - all graphics, game settings etc. identical, no relogs. 'Cos I'm useless I did not note the co-ordinates.
Not sure if it's relevant, but I noticed the signals in the SRV were listed neatly in type order, with all the polyporous appearing first. I'd always imagined the list order was related to distance - guess not.