I have insufficient personal experience to comment directly but understand there are two schools at least.
In the first school there is saturation before six is reached. After the first few strokes the buttocks are hurting about as much as they can so subsequent strokes hardly register. It is unclear whether the acute pain lasts longer when more strokes are given but it is likely there is more soreness after and certainly more bruising.
In the second school the last strokes are the ones that really tell and bring a boy close to breaking. “Anyone” can take four but a boy has to be a “man” to take a full six and anymore than that is too dreadful to contemplate.
Possibly, the phenomenon of saturation is common to all but it occurs at a different number of strokes for different boys.