Question about AL math and FM cashin

Hi,

So far in my C12,C34,and m1, I got 482/500 and an A* in C34 so in my last module, i don't need any mark to keep the A* (since i have 482 already and an A* in C34) my question lies in the Further math A-level, it says that a requirement is to get 270/300 in the best 3 A2 modules to maintain an A*. So i was wandering if the cash in system will take the best 3 modules for the A2 Further math since even if i score a zero in the last A2 math module i would still get an A*.

for example, i have m2,m3,fp2,fp3. so would the system get the best three of these and award it to the FM and leave the fourth unit to the regular math or do I have to personally specify which unit to assign to which subject?

thanks in advance for helping