Haha... you're trying to make a brick from soup here. The APS points we use to allocate numbers to sub-levels are worked on the theory that the mid (b) level is calculated as 6 x level + 3. Thus, 4b is 27 points. Accordingly, a 2b would be 15 points. Whether you can link a sub-level to even numbers of points, I'm not even sure. Whether it really means anything, I'm certain about!