> The congestion window size is calculated with the formula cwnd * 2^wscale . In the output above, notice that wscale equals 7 , and cwnd equals 10. This comes out to 10 x 2^7 according to the formula, equal to 1280 bytes.

That's just not true.

If the author is reading this - cwnd unit (in linux) is in packets not bytes. I'm not sure where they got the formula from (that's the receive window scaling formula, and has nothing to do with cwnd), but iirc slow start defaults to 10 packets. With their mss being 32K (a loopback connection) the actual cwnd size in bytes is at least 10 * 32K.