Thanks for clarifying. I no longer look for compression at all on layer 1. I'm actually looking for the print nozzle to be exactly the right height from the bed in order to create a perfect first layer with the right spacing on the infill (i.e. no holes and no ridges). It seems that no amount of careful setup locks this in for me and (almost) every print I have to use z-nudge to tweak things until I get what I'm looking for. 3000 mm/m is 50 mm/s so 20 mm/s is for me a 40% first layer speed, which doesn't that slow, and isn't far off what I do with a 50% first layer. I just can't believe PLA is going to stick at 55 degrees with a 40% first layer speed, but I'll definitely give it a go. Perhaps the combination of slow speed and compression is helping. I also let the heat soak over the whole plate, though I don't time it and it's almost certainly not a full 30 mins.