Iceberg above a certain price

[buyshirts]

So i want to monitor a market where im looking to back an outsider. I currently have a £10 in at 690 but the best lay is 320.
So if any money comes in to lay at 550 i want to take that up £100 and i dont want to leave any backs in lower than my 690.
So i setup place back bet i used parameters Best market price Fixed amount of £2 fill or kill 0.5 seconds.
Conditions Lay Price of Nominated Selection greater than 540. Number of unmatched on current selection less than 2.
But when i run it,it took bets dow to 320 (where the lay money was) .
What am i doing wrong?

As usual any help is much appreciated