I've seen the 400-500 lot flasher before, shows up right before a big momentum move. 400 some odd lots showed up on the bid at 106.99 around 11:52-11:53 with price at 107.08, before the move to 108.24. I bet if you watch the book from 11:43-11:45 some bid size spoofed also.
From 11:15-11:41 was an interesting period, seemed like someone had both sides bracketed. With price moving back and forth between 106.48-106.62 range,There were 80+ lots on ask at 106.62, 106.64, 106.66 each. Below the range, 100 lot was at 106.50, it got hit into, then at 11:29 price tagged 106.48, it moved higher a few ticks, then 120+ lots showed up at 106.48, 'defending' it I suppose. Price broke out higher after that.
Some notes I have from Friday 3/9/12, that same 500 lot flasher was there each momentum move higher. One time 180 lots, another time 550 lots showed up a few ticks below best bid just a few seconds before the momentum moves higher. 524 lots at 9:49:44 before a 30-tick upmove. The 108 levels that got rejected at 10:41, 10:58 both had 100 some odd lots sitting above.......
All that being said, I haven't looked at all my recordings yet, but I'd imagine every move has size sitting above or below, not sure how to determine which ones will hold or not.
I was short 11:01-11:02 this morning because there was size (believe 90 lot) at 106.36. But they barreled right through that one.
At the 12:23 HOD today, there was a 212 lot sitting at 107.40. I shorted 107.30, took it off for 10 tics.
Now my head will blow up from watching size levels. Thanks for reading.