when/how much hop extract to use?

[Blinky]

Im making an American IPA - hoping to come out around 7% (So not a session ale!) and the recipe I have been give has an ounce of chinook, cascade and centennial in at flame out and the same for a 7 day dry hop (I used Magnum in the boil for IBU's, about 50 of 'em).... As I never seem to get the massive hop aroma and flavour I also bought Hop Sensation Deep Sea - 10ml Hop Oil, it says to add after fermentation and between 3-10ml. I was thinking of going with 4ml, at the same time as bottling, so add it to the bottling bucket and siphon from the FV on top of it, does that sound like the best plan? Never used this stuff before, thats all....