When I use blue foam, there is some space between the bottom of the blue foam and the bottom of the cartridge. To do a long-lasting fill I remove it, fill the cart about 1/2 way or a bit more with juice, replace the foam and push it into the juice, pull it back up with an unbent paperclip and reposition, then top it off with a drop or two. I usually do that a couple of times per day. The rest of the time I just top it off by adding a couple of drops on top of the blue foam.
Drip tip is different - it slips into the atty instead of a cart. You drip 2-3 drops into it and it goes on the atty. You vape that and when the vapor gets low you add 1-2 drops.