I can add two things i had to "workaround".
Both occured in small facility with a less than 50 guards. My different attempts and tests were started from the same save and played for days, to be sure that game reached the"equilibrium" after the change.
1: I could not make my two small staffrooms to have food delivered simultaneously.
Double-checked, with staffroom/staff canteen scheme, always checked if given room is still "staff only" and so on.
Workers delivered crates of food to one serving table up to its full capacity (four crates, circa 50 in each) instead of equally using the given number of serving tables. And it looks like the amount of food delivered has connection to number of staff - even if the tables were in the same room, they started using the second one only when I added (for experiment purposes) another 50 redundant guards.
So, workaround: I had to rebuild prison in order to have one bigger central canteen instead of 2-3 small ones, loosing effectvity *.
2: Cooks carrying clean trays, on the contrary, deliver it to every serving table in any "staff" location.
But not in the way they do for inmates' canteen, where serving tables are always fulfilled to the 50 - 70 trays each, even if it leads to 200 - 300 trays for 50 prisoners. Instead, when serving table is empty, cooks are triggered to go for one pile of trays to kitchen. And they grab one pile from sink. It can be - in small prison, remember - a pile of 10, 20, 2 trays. Checked: if the same canteen,or even more remote from kitchen, is not "staff", they can fulfill it to 50 without difficulties, so it is not a logistic issue.
I see nice workaround here in this video, with sink placed in the canteen and cook doing the whole job inside the canteen (I didn't thought about it ;-( i placed second serving table - redundant, as written above - only for purpose to "statistically" raise the amount of clean trays in canteen area and lower the probability of both tables run empty).
EDIT: it works as charm, i hoped just for shortening the route of trays to sin and back, but after a connecting kitchen to staffroom it finally forced the cooks to stash the trays on serving table up to 50 as elsewhere!
* by the way, time needed to travel across the area is a bit unrealistic when you start to look at it closer: young fresh guard sacrifices about half of hour of his own break just to travel 40 meters of road and 70 of concrete tiles (in stab vest). But imagine all of them guys going 3x faster, or time flowing three times slower - it would hurt the gameplay, so let it be for sake of playability.
But, I really prefer to have multiple small stafrooms, more cooks and workers to supply, and give them the longer walks, instead of guards wasting their time for longer breaks, walking back on position and so on. Safety depends on guards.