My Bolle The One sits so low the bridge of my sunglasses fits right against the brim of the helmet. No "forehead gap." It is kinda wide, though.

Kask helmets sit fairly low. The Oakleys fit like hats-- so they feel like they "sit on top." I personally think those Giros make everyone, regardless of head shape, look like an acorn head. They sit high on everyone.

I buy each new helmet by just trying on all the helmets and buying the one that feels the best. I don't look at the prices first. I trend to cheapness, and will sacrifice comfort for cash if I know the price in advance.

Mountain bike helmets cover lower on the skull. Try a few and see if you like them. I did a couple of weeks ago and was pleasantly surprised to find they fit well, were comfortable on my Frankenstein shaped noggin, and had clearance in the back for my ponytail and bandanna knots, while still covering the base of the skull more effectively than most road bike helmets.

However I got a Bell Formula MIPS, mostly because I wanted a hi-vis yellow helmet and it was among the few REI had in stock in that color. There was also a very comparable Giro, but I got the Bell. Not much difference between 'em, although the Giro strap is softer, more comfortable and less fussy.

My older Bell Solar was more oval shaped, which initially seemed better suited to my skull. But the newer Bell was shaped more like the Giro, and both of those were comfortable as well. No complaints after two weeks and a few rides in summer heat.

The Bell Formula MIPS seems more minimal than the Bell Solar, but that's due in part to less stuff protruding out the back. It probably still offers adequate coverage. But if I had to go with a mountain bike helmet instead that would have been fine. They fit well too and didn't look dorky once the visors were removed.

To me, this pic grabbed from Kask's website, has the rider with a slightly too small helmet; and this doesn't look like it's sitting too far down on his head.
I have a mojito.. one thing to be aware of, there's no way to adjust how far down the straps meet the V under the ear. Can be a problem if your ears are lower on your head than Kask thinks they should be as you end up with the straps crunching your earlobes.

The adjuster on the back of his helmet looks to be all the way out-- like his head is at the intersection of S/M and M/L, so he wears the smaller size opened all the way up, presumably to save a few grams. The Vertigo and Protone do seem to sit closer to the ears. My Vertigo 2.0 does, for sure.

quite surprised marketers havent segmented their models into general fit, in the way that fizik does with their snake-bull-giraffe-unicorn saddle system

Just a suggestion...

It might be worth trying the POC Trabec helmet. I bought mine because it was the first MIPS helmet I got my hands on that both fit and was a color I'd buy. (I will only consider white and yellow helmets.)

It has much better coverage than road helmets. I've been wearing it for 4 years and love it. Very comfortable. I put it on and forget it until I take it off.

Ben

I just bought a Bontrager Ballista sized small because I was between that and medium, and it ends up sitting slightly too high over my temples like OP is worrying about with his helmet, though in my case it's because my head is wider than it is deep. I think the medium size would be too big though, so I'm fine dealing with the helmet otherwise.

The Bontrager helmets like the Ballista have a way to adjust the back harness height. I know with my small, it was already at the lowest setting, so I can't get it to sit lower on my head, but maybe you could try adjusting a medium-sized Ballista to sit higher for you?