"Narrow profile stylus" isn't an accurate term to describe the stylus used on the Helikon Mono, as it isn't intended to be narrow. On the contrary, it is intended to "fill up" the LP groove as completely as possible without triggering difficulties in setup. "Long contact patch" is a much better way to describe it.
IMO, a proper mono cartridge shouldn't pick up vertical information. A mono cartridge can be approximated by summing the coil outputs of a stereo cartridge together, but this is no better than using a mono switch, and the completeness of cancellation will be limited by any dissimilarities between channels (encompassing those caused by setup as well as build).
The stylus on the Helikon Mono isn't an Ogura PA, as the scanning dimensions of a PA are 3x30um, which is considerably narrower than what is actually used.
The prototypes of the Helikon Mono started out with a 3x30 PA, as that was the same as what was used on the Helikon stereo version at the time. We extensively tested a variety of stylus shapes on both new mono and older mono LPs (some of these dating back to at least 1953~54), and found that a custom variable-radius 3x70um profile was the most to our liking - on everything. And that is what was incorporated into the production version.
Later we found that the custom 3x70um stylus gave better results on stereo LPs as well, so we gradually shifted from the 3x30um Ogura PA to the new 3x70um stylus for all of our cartridges, stereo as well as mono.
The only exception is the entry-level Dorian, which uses a Namiki Microridge 2.5x75um for both the Dorian stereo version and Dorian Mono. I chose Microridge for the Dorian because it was the closest production stylus (meaning less expensive) to the custom 3x70 stylus used on our more expensive models.
FWIW, I don't believe that groove width means much for a wide, long-footprint line contact stylus. The important factors are groove angle and groove depth. The groove angle of a Microgroove LP should be 90 degrees, and as long as it remains 90 degrees, the stylus will simply keep its natural distance (as defined by the stylus shape) from the groove bottom, and should have no problem with remaining in full contact with the groove walls or tracking, regardless of groove width. If the groove bottom is shallow, however, or filled with dirt (not an uncommon condition with second-hand mono records), the tip of the stylus may "bottom out" if it is too acute and goes too deep.
Bottoming out was one of the primary reasons why we rejected the Ogura PA. Our custom 3x70um stylus retains a longer contact patch with the groove wall than the 3x30um Ogura PA (which is the essential thing for performance), but doesn't go quite so deep and therefore doesn't get into problems with shallower grooves.
hth, jonathan carr
