Not a Member: I am the author of the 2nd thread you are referring.
Pine trees are not always present, but they can acidify the soil. Unofortunately I have never checked the Ph of the soil, but it should be acidic, because you can always observ acid-soil lover plants in a community.
According to my observations, I can confirm this: "During our observations in its native habitat, we have never seen Drosophyllum growing in alkaline soils, despite several intensive searches at suitable places."
I have only seen DL in three natural habitats in Portugal, but the soil was more rocky, without limestone, but sandstone was observed two times of these localities.
Let me share some photos, taken last spring in Portugal just to show how is their surrounding and soil:
Drosophyllum lusitanicum growing under pine trees, sorrounded with rosemary and sandstone in the background
Sandstone, just some meters from plants
Heather-bell? (Erica cinerea?) Quite likely to observ together with D. lusitanicum. This heather likes acidic soils.
Drosophyllum and sandstone
DL with a dwarf oak tree
Drosophyllum with dried Erica flowers
Surface of the soil (quartz sand)
Shrubby environment with quartz sand
Flints with quartz sand
A different site, I found the plant with red sandstone in loamy soil
So if You guys are coming to Portugal, already known the signs to look for :-)