Good for you and the bus company. School buses are the worst offenders for passing too closely, in my experience. I will try your approach next time it happens, if I have the wits to see and remember the bus number.

There is one school bus that passes me regularly right before a RR crossing and comes to a complete stop, as required by law. Seriously, the bus passes me within 20-50' of the crossing nearly every time -- forcing me to stop. The bus driver could easily wait 1-2 seconds and avoid passing me, but does the same thing several times a week.