If it's a 1L flask you are using only put 650mL of wort in there...
But I've had it work with even less than that.... (I was aiming for that so I mixed up 1/2lb and accidentally made about 1.5L of wort so I had to dump more than half of it
Great, thanks a lot. I'll probably use a little less than 1/2 lb. but like you said, I only make about 800 mL starters in my flask otherwise its just oine big wicked boilover.