I've used both the 1/4 and 1/8 tapers listed above and have no issue with them. If you cut to the same depth as the ball end radius you should get a line that's as wide as the diameter. I usually cut 2-4x that deep and the line does get a little wider but it's only noticeable in the finer details.
I do think the 1/4" Jerray cuts better than the 1/8" Chinese ones, but there isn't a large difference. I mill band logos on oak that's about 60x48mm and get reasonable detail with the .5mm Jerray.
This is an extreme close up and the limit of what I can carve with the .5mm bit. I've managed a little finer detail with a .25mm bit but I'm at the mercy of the wood grain as to how much detail survives. This was carved at .7mm depth one pass. Post-carve the wood is barely sanded, brushed, and painted. When the paint dries I sand off about .25mm to reveal the detail, then finish with mineral oil.