You tried plain blue foam? The blue foam should be very slightly wider than the
juice cup (just a smidge for a tiny
juice cup) and I cut them about 3/4 the inner length and a bit tapered on the inner end. You need to keep it at the top of the juice cup - if it won't hold itself up there, make it a bit wider. A full fill with blue foam is remove the blue foam, fill the juice cup 1/2 way (2/3 if you are daring), stick the blue foam in and push it down into the juice to wet it. Reposition at the top edge of the juice cup, then top off with 1-3 drops (whatever it needs to look just damp on top, not a puddle).
And if you have carts that push on over your atty, do not use the atty to push the juice cup back in - especially if it is a pointy atty. The atty will just shove the stuffing down too far into the cart. You need to get the juice cup back into the mouthpiece WITHOUT pushing on the stuffing.
What ecig are you using?