hi, I think it depends where you are!
In England you must spend 6k annually on interventions, SEN TA support etc before asking for top up funding. It’s your “element 2 notional budget”. Then you can apply for moreafter showing how you’ve spent 6k to no avail – but each LA has a different system for this. I work in Derbyshire where we apply for GRIP / Taps but previously I was in Staffs and it was AEN funding.
Next step is EHCNA. Even then the amount is quite variable, unless you have special school categories.