sgolayfilt function use the whole sgolay matrix?

Hi,

I recently started trying to port sgolayfilt() into my own c code. I realized through looking at the sgolayfilt function that it uses the whole matrix instead of the center row/column to do convolution with the data. Following sources like wiki, the convolution between the data points and the center row/column of the sgolay() generated matrix should be enough, but Matlab seems to use that for only the middle of the data, while the ends of the convolution uses the top and bottom of the matrix. I was wondering why that it is the case, as it seems to provide better results.

Thank you for any help in advance.