Max power possible from 6L6 with 6.6k load?

In the '6L6GC AB2 Amp' thread George (Tubelab) posted some impressive max power results:

VG2 - 400V VP - 500V Idle current set to 65 mA per tube.
3300 ohm load yields 91 watts @ 3% and draws 175 mA per tube
6600 ohm load yields 57 watts @3% and draws 110 mA per tube
13200 ohm load yields 29 watts @3% and draws 78 mA per tube
Triode mode VG2 = VP = 450V idle current 32 mA per tube
3300 ohm load yields 57 watts @ 3% and draws 145 mA per tube
6600 ohm load yields 41watts @3% and draws 95 mA per tube
13200 ohm load yields 25 watts @3% and draws 63 mA per tube

Click to expand...

Anyway, I was drawing some load lines trying figure out if I should be impressed or not and I can't figure out how it would be possible to get 57 watts with 6.6k and 65mA bias at 500V plate and 400VG2.

I have attached a load line for one tube.

The issue is that with a 6.6k plate to plate load the most current swing one can get(in a half cycle, if one could bring the plate to 0V) is 303mA - 65mA which is 238mA. P = Irms^2 * R or (.238 /1.414)^2 * 1650 = 46.7W. I'm being overly generous here by letting the plate swing to 0V. I have not taken into account distortion, but it is only three percent.

What am I missing here?

See this thread for more information.