Geeetech A20 + BlTouch = first layer height question

[navzintel]

Hey,

i got an A20 from Geeetech and upgraded a BLTouch to it.
I followed the instructions to setting up the right nozzle height.
I adjusted the Z-Offset until a piece of paper (round about 0.1mm thick) is slightly
scratching on the nozzle when Z = 0mm. Therefore my nozzle is 0.1mm away from the
heatbed. Now im slicing a STL with 0.15mm first layer height. Accordingly my nozzle now
should be 0.25mm away from the heatbed. Am i right?

My problem is, the first layer wont stick well enough on that height and my nozzle seems to just
lay down a line of PLA on my bed and pulling it around the heatbed.

Did i missing something? Do i need to adjust my z-offset, so my nozzle is touching my bed or do i
have to adjust my first layer height in Cura to near zero, so my nozzle is 0.1mm away from the bed
on the start of printing?

Greetings from Germany.