No, you need 4 followers per city.
Actually Tithe is far better than that. Testing it out tonight it appears that it's based simply off your total number of followers across all cities, it doesn't have to have a minimum of four per city just to get a 1g bonus.
City #1: 6 Followers
City #2: 4 Followers
Cities #3 & 4: 3 Followers
Cities #5 & 6: 2 Followers
City #7: 1 Follower
So if it were 4 minimum per city I'd only be receiving gold from the first 2 cities at 2g total.
But instead im gaining 5g per turn from religion (tithe is my only gold granting religious bonus) and that fits if you take the total number of followers across all cities added up which is 21 (which when rounded down to the nearest multiple of 4 is 20 or 5g per 4 followers).