[James98]

How?? I want more underboob but i cannot position the cups lower down or else it hurts! Or the whole boob gets sucked in! Im yet to learn how you can vary positions

Try using a much smaller cup that only covers your underboob (chest to just below nipple). 
Other option is to force the cup lower on your chest, but this is very difficult to maintain. 
Third variant is to lie on your back so your pelvis is higher than your shoulders, so your breast falls upward in the cup.
Fourth, lubricate only the bottom half of your breast, this way the top will not expand as much because it will not slide out in the cup.