That's right, you do. That seems to have been a factor in that in the past, government parties' redistricting and redrawing of boundaries was done by the government of the day, in effect. Back in the 1940s the government of the day brought in a new system under which five seats was the largest constituency size. That seems to have been accepted as the norm, even though these days redistricting is done by an independent commission, and it's always given terms of reference under which five seats is the largest used.
On July 26th, 2016. See this statement in context.