I am using Neco headsets from Peter on both frames.
The last time I had the headset apart, I measured the OD and ID of both the headset bearings and integrated cups, the lower bearing was perfect with nearly zero gap, but the upper bearing has 0.2mm of gap, which is the movement I'm feeling. However, when I check the tolerances for the headset and integrated cup they are in spec, though at the larger end of the spec, which is the 0.2 gap.
DIdn't have time to look into this any further tonight but it's not high on my list as it doesn't feel as bad after packing it with grease.