Maybe friendly is not exactly the right word here. I'm talking about smoothness, good manners and things like that.  

There is a difference between Lahti (population 118,000) and Tampere (population 225,000). People in Tampere tend to have slightly better manners, on average. But the biggest difference is the difference in the standard deviations in how well people behave measured by, for instance, the frequency at which someone will say something rude to you. To give you an idea of what I'm talking about in quantitative terms, my impression is that if a certain level of rudeness is achieved, say, by one percent of the population in Tampere, that same level of rudeness would be found in three percent of the population in Lahti. At the other end of the spectrum, if a certain level niceness is achieved by one percent of the population of Tampere, that same level is achieved by two percent of the population of Lahti. This implies that how well-behaved the people you meet in Lahti are will depend more on the individuals and their upbringing than in Tampere where there seems to be more of a general tendency to maintain a polite distance to a greater degree. 

I have visited London, UK, eight times. During all of my visits, people were using polite words and being flexible and adaptive all the time, and I started to follow their example.  I also noticed that in Stockholm, Sweden, the general atmosphere was very relaxed and friendly, moreso than in Helsinki.