Yeah, I have also known multiple tattoo artists who won't do color fill on really small tats, because without regular touching up, they bleed and fade and warp drastically.
I'm going to get this logo of the Scottish Great Trails as lineart, and I'm hoping to fill in the three segments as I do the three trails on my bucket list (West Highland Way this year, John Muir and Great Glencoe Way in the future)
Oooh, an aside, but the John Muir trail is amazing, I've only done part of it for obvious reasons, but hands down one of my favorite trails in the country.
I'd say go bigger if you can, but then you could always insist on smaller and still fill in the lines as long as you're prepared for how much they'll fade/will need touching up
I would talk with the artist you're thinking about working with and see what size they would feel comfortable filling in, like the smallest they would go
see if that works for you, since at some point the space between segments is definitely going to bleed together and become one piece at the size you're asking for.
I think it's worth discussing with your artist! I have a couple smol bois filled in with black that are about 5-6cm and they aren't doing too badly. The one on my finger definitely needs to be retouched but it's been 8 years in a high-traffic spot