Okay, here's the scoop. First of all, Koman, it boggles my mind how one would mod a cart to make it hold more juice.
Second, Amy, forgive me for straying, but I had to get just one from an American vendor to see if I like them before I get more from you when you stock them. Anyway, the carts hold more like 1.25mL, which is plenty. I got it to wick well by doing a straw mod and trimming the poly fill that came with it vertically, about as much as would take up space where the straw now is. They put too much fill in the carts in the first place. It wicked all the way down until there was only .1g left held in the fill. Only once during vaping did I get the nasty burnt taste, and so I just took a tiny bit more time between drags and it was fine.
The bottom line is, it's a trade-off between mega XL and mega slim. The mega slim does not leak, at all, and wicks well enough with the mod, and looks nicer. The XL hits a tiny bit harder, IMO, holds more juice, and can leak if not stored properly and overfilled. Solution, don't put more than 2mL in it. Lay it down until enough juice is gone, or stand it upside down. I also straw mod these and then the poly fill works fine. I find the Hagen foam does not hold the liquid well enough. Some "EXPERT" in the ask the experts forum told me it would solve all my cart problems. AS IF. If I could just breed the Hagen filter foam and poly fill into some ....... child that would have perfect liquid holding capability along with good wicking...well we would have a good frankenfiller!...LOL
SO there you have it kids, I am happy with both, maybe you will be too.