Just want to clarify what happens with LA's of 4, 5, and 6?
Taking an LA of 5, for example. The first level this can be bought off is 15. Which will bring it down to a LA of 4. So when do you buy off the next level? Using the usual method, the next LA would be bought off at level 27 (4*3+15). The ratio isn't 3:1, so you don't have to buy it off straight away.
Or... I'm not swapping between ECL (including LA) and actual CL correctly.
Because even though the characters ECL is 15, their actual level is 10. So, after buying off one LA, once they hit ECL 16 their actual level is 12, which is a 3:1 ratio with a LA of 4.
But then they're at ECL 15, an actual level of 11, and a LA of 3.
I'll just stop, I'm confusing myself now.