I am a low time fretless player, 8 or 9 months now, but I've played fretted for awhile, starting in '72. I had difficulty going to the upper octave when I was learning fretless on my lined SR370EF. I think the reason is the lines distort up there as viewed from my perspective on that bass. When I acquired an unlined fretless, the Sadowsky MX Fretless Hybrid, I actually found it perhaps easier to play in the upper octave. Reason, I was just relying on my fingers and my ears without trying to position my fingers to the lines anymore. The upper octave is easier to hear. Distances are smaller, so if you hear a flat or sharp you can correct with just a roll one way or the other. One finger width generally equals one semitone. Not rocket science.
For some strange reason I seem to also land the long range shifts more accurately up there. No idea why.