>>In the scenario you describe, I cannot see any actual amplification...

I'll give you a senario where you can see.

lets say you have 2 name servers that are local to you.

I setup a domain, example.com. In this domain I create a text record =
which is 100K in length, I don't know, perhaps I paste the source code =
to decss in it, whatever it's a big text record.

Now I simply spoof a UDP packet using your IP address as the source =
address and send it to both of your dns servers. This packet is a query =
for the example.com text record. I have now sent two very small packets =
and you have received 200K of traffic. That's the amplification, one =
small udp packet, one large text record in return.

Note, I don't have to use your local servers, but this way it makes it =
more fun to troubleshoot because it looks like you are the cause of your =
own flooding..

Geo.