Of course size matters. Finland’s homelessness likely coalesces around its largest urban areas, as they provide the most foot traffic and anonymity (and homeless services) with the least annoyed population. Like in every country.
So most likely Helsinki.
If your pool of possible homeless is 5M and they gather in a city the size of 600k it is a hugely different situation than say San Francisco, which is 800k and draws from 330M possible homeless