From a cursory glance, the math seems right.

As far as granted levels go.
For every 60 you level (from 1st), you can boost 30 levels.

If there is one link in the chain...
Example A -- B
You would need to level two toons on B, to equal one 60th on A.

If there are two links in the chain...
Example A -- B -- C
You would need to level four toons on C, for granted levels on B (from C) adding up to a full 60th on A.

But if you are going to partially level toons.
So the granted levels, plus partially leveled toons, add up to 60th.
Then cascading the granted levels isn't that big of a concern.