Granted levels do cascade.
But because you are granting to a toon of your level or lower, it is a trickle down effect.

For example:
A >>> B >>> C
A >>> D >>> E

A boosts BCDE, from 1st to 60th.
B can grant 30 levels to A, and D can do the same, and since they're both 60th, they can combine for a new 60 on A.

C and E, each grant 30 levels to B and D.
Based on these granted levels, B and D can each give A 15 more levels.
But B and D have toons who are level 30 at this point, so cannot use the 15 levels to take toons beyond 30th level.

However, if A were to boost another set on BCDE to 60th.
CE (level 60's) can give another 30 levels to the same toons on BD.
And these toons, now 60th, can each give another 15 levels to A, for a total of 30 levels granted (each) and a maximum granted level of 60th.



Summary...
If you boost 2 sets of toons, for every step in the RAF chain, the levels cascade into full toons.

X -- 2 -- 4 -- 8 -- 16

X -- 2 -- 4
X -- 2 -- 4

X -- 2
X -- 2
X -- 2
X -- 2