Think of this as you being a distance (vertically, of course) from a pressure level. Take the 1020 pressure level. If you have 1020 set on your altimeter and it reads 300ft, then you're 300ft from the 1020 pressure level. Now set 1010. The altimeter reduces by 300ft (where'd this 27ft/mb come from??) because the 1010 pressure level is closer to you.
Sama Sama if you set 1030; you are measuring the distance between you and the 1030 level, which is further away than the 1020 level. This is indicated by an increase in "altitude".