After some more tests I guess I meanwhile know better and clarified my confusion 
The table values are right and make total sense. My initial thinking was that if I want to switch from e.g. PLA as support material and to avoid instability in the PETG layers, I need to flush out lots of PLA, which for sure isn’t achieved by increasing the PLA flushing volume but the one of PETG, i.e. the table cell “from PLA to PETG” should have the increased flushing volume.