25% initially is the max can be allocated automatically every month. Eg. If ur primary gets 100GB; secondary will get 25GB fixed every month.
One that is exhausted or even not, you can still manually allot more but only in 25% bifurcation meaning after initial 25GB when ur primary data Balance is 75GB the next transfer will be of 18.75 gb and so on.
I believe you can only do this 5 times every month.
For Vi, 200GB is the max you will ever get; your rollover pool and current pool is the same. This will be the same for child as well.