All packets in the session after the S-S/A assume the negotiated scale for their direction. OK, so 262144/8 = 32768. That's the correct window value, assuming you are still signaling a complete window. This is also assuming you are sending the ack from the same direction as the S/A. If you are sending it from the other direction, you use the wscale advertised by the SYN (if it was different). I am still confused on how you plan to 'insert' this ack into the session. The receiving stack is going to generate acks for all data received. How are you going to decide the sequence number to acknowledge?
fnord