I too was quite surprised about all the complex science there is behind a successful cartridge design. In most fluid dynamic applications, a difference of a couple inches in the altitude of a fluid in a non-pressurized vessel makes little difference in the static pressure at the discharge point.
However, there is a very narrow range of acceptable parameters in a inkjet cartridge, ink and print head combination. The ink formulation must have the ideal viscosity to successfully flow at the correct rate via a combination of gravity and capillary action from the cart though the print head, whether the cart is full or nearly empty. If the ink viscosity is out of spec the ink will either be so thin it siphons out through the head on its own -- even when the printer is not turned on -- or so thick that the flow volume is insufficient to meet printing demand and the print quality will suffer. This is why ink formulation is so imortant to refillers and finding a high-quality/consistent ink manufacturer is paramount.
But cartridge design is equally important. Discharge pressure and flow has to meet the specs of the print head regardless of ink level and while the cart is rapidly moving back and forth during a print job -- shaking up the ink and forming foam and bubbles that will create an air lock in the print head if allowed to make it that far. The traditional method of preventing this is to use a sponge-like material that uses capillary action to draw only the ink while the air naturally rises to the top of the sponge chamber and out the small vent port at the top.
Epson OEM TO48 carts (and probably many others too) still use this simple but reliable cart construction where about 2/3rds of the cart is sponge chamber leaving only 1/3rd for the ink reservoir. But manufacturers of Epson compatible carts have successfully engineered a spongeless design employing a network of internal passages and a small regulator tank to take the sponge's place, and greatly increasing the volume of the ink reservoir. They work great and significantly increase the number of prints between refills.
But so far, sponge-less Canon compatible carts have not been proven to perform as well as OEM carts, so the OEM carts remain the choice of experienced refillers. Since Canon print heads use heat to eject the ink jets and will quickly overheat and burn out if the ink flow to it is insufficient, it is risky to gamble with a cart that can't match the performance of the OEM cart. Since Epson print heads run cool and use ultrasonic energy to spray ink, experimenting with compatible carts is much less risky since the head isn't subject to a burnout if starved of ink.
Long story short: Unless and until a suitable compatible cart is available, Canon OEM carts remain the best choice for refillers... :iagree: