It is my understanding that 7.5% is the cap, which should only be reached when you have very little dependencies.
If you have 20 direct dependencies, each one will get 5% only, including StackAid.
> When reallocating funds back after numerous project won't install some github app to claim the money collected on their behalf, are the 7.5% kept?
The answer is on the site: The funds are held for 2 months, then reallocated:
> A project's allocations accumulate for 2 months. If the project is not claimed by then, an automatic reallocation happens and the amount is redistributed to the other dependencies that are claimed. Reallocation occurs on a per subscription basis.