I am a first year engineering student and I have conducted an experiment with other students.
I know that the contact area of an object to a surface does not affect the coefficient of friction given that the object's weight stays the same. But what if the position of the contact area is changed? Shown as the photos below, the contact area is distrubuted through the face of an object while remaining the same value of contact area. We did the experiment and it's shown that it doesn't matter, the angle needed to slide the board pretty much remains identical.
My question is why does the position of contact area does not matter? Is it simply because the contact area is just the same? I want to conclude the experiment but I need help with an explanation referring to mechanics theory.