Not tried - just as idea. Create this expression twice and put the second one on the second axis, customize this axis a bit lower as the first and hide it, show your figures but hide this line or make the color transparent. Another possibility could be to put two charts one above the another and hide from one all unless the figures - but by many charts is this not very nice.
thanks for the idea! However, I already have two axes, so that won't work.
"Moving" the axis using the minimum/ maximum settings didn't work yet for me, either.
Well, I have been able to make it better at least in the meantime by making the fixed target_line dotted and making the figures black, bold and a bit bigger. It's not optimal, but now the figures can be just about seen.
Thanks a lot!