Back when I used cartridges (straight dripper now) I found that they were overstuffed. I would cut the stuffing in half so that it wasn't sitting right on the atomizer and push it down in the cart about a millimeter (but not too far down or it won't wick...). drip on the filler until it is saturated (looks a little mushy on top, but not like the liquid is sitting on top).
On the other hand...the flavor dripping is so much better...usually a 510 will hold 3 direct drops (5 if it is new and you're dripping on it for the first time).
Hth...