My question pertained not to spreads but to the precise trigger of the stop-buy, be it the ask price, a buy-ask median, or something more fuzzy. My eyeballs tell me the stops are triggered when the Bitcoinica ask is above my stop-buy, but I do not know for certain whether the ask is the precise trigger.

I sacrificed a few dollars when the Mt. Gox ask prices rose from $2.92 to $2.95. Bitcoinica charts show a wee bit over $2.94 and the Bitcoinica ask is currently a bit over $2.97 and the spread is about $0.8 at this moment: