Bradley Adaptive Thresholding -- Confused (questions)

I have some questions, probably stupid, about the implementation of the adaptive thresholding by Bradley. I have read paper about it http://people.scs.carleton.ca:8008/~roth/iit-publications-iti/docs/gerh-50002.pdf and I am a bit confused. Mainly about this statement:

if ((in[i,j]*count) ≤ (sum*(100−t)/100)) then

Let's assume that we have this input:

            width, i
            [0] [1] [2]
           +---+---+---+
height [0] | 1 | 2 | 2 |
j          +---+---+---+
       [1] | 3 | 4 | 3 |
           +---+---+---+
       [2] | 5 | 3 | 2 |
           +---+---+---+

and let's say that:

s = 2
s/2 = 1
t = 15
i = 1
j = 1 (we are at the center pixel)

So that means we have a window 3x3, right? Then:

x1 = 0, x2 = 2, y1 = 0, y2 = 2

What is count then? If it is number of pixels in the window, why it is 2*2=4, instead of 3*3=9 according to the algorithm? Further, why is the original value of the pixel multiplied by the count?

The paper says that the value is compared to the average value of surrounding pixels, why it isn't

in[i,j] <= (sum/count) * ((100 - t) / 100)

then?

Can somebody please explain this to me? It is probably very stupid question but I can't figure it out.