Ferro fluid replacement on 1" dome tweeter

Frist time trying replacing ferro fluid on old 1" soft dome tweeter and seek kind advice from experienced members.

When I google, there are several different ul (microliter) such as 100, 300, 650, 900ul. If I replace 1 inch dome tweeter, do I just need 100 microliter per each 1 inch dome tweeter? It looks like 300 ul is the most popular one from the number of units sold somehow.

And, how much filling the ferro fluid? My guess is that it is not to fill all the way up since voice coil needs to be going in then it will overflow.
Do I fill about half way and it is about right?

Thank you very much in advance and any advice would be hugely appreciated.