Too bad the saints seem a bit limited in their mathematical abilities. Even if they multiply their resources by 5, or to be generous let's make it an even 10, they are not going to be increasing the size of a purification circle by as much as they think.
Let's assume things in their favour, like that it is not a magical technique that does everything over a circular area, then it is a bit cheaper. Instead we only need to consider a purely 1-dimensional circular circumference. If we are this kind to our math, then yes, the radius is linearly proportional to the circumference. So having 10 times as much resources should lead to 10 times the circumference, which in turn is 10 times the radius. But even then I very much doubt it is enough to cover an entire continent, as the country (the area she covers right now) needs to be a full fifth the size of the continent, OR located in the center in which case it can be a tenth. Which is unlikely.
And that is when stacking everything in their favour. I am fairly sure the purification circle affects the area inside the circle too, meaning the radius is not linearly proportional. And so the radius should be only sqrt(multiplier) larger, which further makes it so the country needs to (approximately) be somewhere between a third to half a third of the entire continent. And if the factor of 10 times more resources (mana) is too high, things further devolve.