I once worked at small org with a dozen people, and one person was "support" role: she was finance, admin, facilities etc.. We did have cleaning services from our landlord and separate legal and tax, but they were nowhere close to full time.

In another place we had maybe 30-40 two person offices, and 3 of them were occupied by HR/finance/admin/facilities etc...

So 1/100 does not sound very realistic (maybe for all-remote orgs?), but 1/10 I can easily believe.