get some totes and put them outside the package cars; when your bins come around, throw the smalls into the totes and just load them when you can
tell your supe you're just trying to protect the smalls with containerization lol
That's not going to work - there's no need to containerize in a package car unless it's a SurePost bag (or helper bags during peak with specific stops).
Other than that - 10 years ago most of my boxline MSDs came to around 230 an hour for a 3 car pull. Little has changed in that time that would materially affect a measurement.
Add a car and make it four, the MSD goes down because there's more walking distance, plus, the cage that normally enters the head of your work area is now at the second car, etc.
Anyway - 4 hours of that is 920 and 5 hours is 1150, and that's 100% effective. We look for 95% or so, so in the real world, drop maybe 45-55 pieces off of that for a typical day.
Your contract, of course, says you don't have to care about any of this. Just follow the methods, use a smooth steady pace you can maintain for the duration of the sort, and you'll find the numbers will end up around the ones above anyway without you worrying about them.