A quick look at the formula for the other categories revealed a pattern, where in fact a step is missing. Let's have a look at the complete picture:
| Good: | 2 + floor(0.5*level) |
| Medium: | 1 + floor(0.4*level) |
| Poor: | 0 + floor(0.3*level) |
These formulas lead to the following table.
| Level | Good | Medium | Poor |
| 1 | +2 | +1 | +0 |
| 2 | +3 | +2 | +0 |
| 3 | +3 | +2 | +1 |
| 4 | +4 | +3 | +1 |
| 5 | +4 | +3 | +1 |
| 6 | +5 | +3 | +2 |
| 7 | +5 | +4 | +2 |
| 8 | +6 | +4 | +2 |
| 9 | +6 | +5 | +3 |
| 10 | +7 | +5 | +3 |
| 11 | +7 | +5 | +3 |
| 12 | +8 | +6 | +4 |
| 13 | +8 | +6 | +4 |
| 14 | +9 | +7 | +4 |
| 15 | +9 | +7 | +5 |
| 16 | +10 | +7 | +5 |
| 17 | +10 | +8 | +5 |
| 18 | +11 | +8 | +6 |
| 19 | +11 | +9 | +6 |
| 20 | +12 | +9 | +6 |