Now,on page 3

**Model 1**is pretty clear, to calculate the probability (of the flipped coin landing on its side )

they consider coin side surface area to the total surface area ratio.

**Model 2**is a bit confusing

it seems that they divide one side of a perimeter (h) by the sum of three other sides 2(2R)+h

rather than the sum of all four sides

intuitively it should be 2(2R) +

**2**h

What am I missing ?

Related question: how do they define cross sectional length?

Is it just a half of the diagonal, as per drawing?

And if that's the case,why would the probability be proportional to that length?

I don't find it very intuitive.

Thanks