I don't know if any AHJ still allows it, but my installers, 15 years ago, avoided the possibility of overloading the buss by installing the PV breakers at the far end, away from where the main breaker (in my case one breaker slot away from the end). It becomes physically impossible to put enough load breakers in the space left between main breaker and the PV breaker that would expose the buss to currents that exceed it's rating. I don't know if there is the technical reason that is practice seems to have fallen out favor. Is it not idiot proof enough?
arnold