I was being handwavy with the values (adding a fixed 20 bytes for header), but let's try something more precise:

    the average packet size was 483 bytes (average data
    length = 441 bytes)

So header size is 42 bytes (483 - 441). Assuming the request uses the same headers, we have 483 / (1+42) = 11.23 amplification.

My point is: this is important, but not a 440x amplification attack.