[2.1.9] Unexpected mixed rocket payloads when custom minimum payload is set

[blu.sta]

In 2.0 I had orbital requests for 400 Copper plates and 400 Iron gear wheels, with no custom minimum payload set. This was intended to be used as a trigger to request a new payload of 1000 of either item if the amount on the platform dropped below the set value.

With the new mixed payload rockets in 2.1, I expected this to no longer work the same if BOTH items were below the trigger value, as a rocket would likely be sent with 400 plates, 400 gears, and something filling the remaining space (fantastic feature btw).
In anticipation of this, I set the custom minimum payloads of each to 1000 to attempt to force single-item-payload rockets, but I'm still getting mixed payload deliveries.

Is there a way to force specific (or all) requests to be single-item-payloads? Or perhaps, if a custom minimum payload is set higher than the amount requested by the platform, that minimum is used to determine how much to send to the platform?
Apologies if this is all expected / intended behaviour, and if I should be trying to find an alternative solution.

[blu.sta]

Below are various tests I ran with orbital requests set for 400 plates and 400 gears, with the assumption that each item is readily available:

- Platform with 0 plates, 0 gears in cargo
Custom minimum payloads = 1000: Requests 1 rocket with 400 plates, 600 gears / Expected 2 rockets with 1000 plates, 1000 gears
Custom minimum payloads = 500: Requests 1 rocket with 400 plates, 600 gears / Expected 1 rocket with 500 plates, 500 gears
Custom minimum payloads = 200: Requests 1 rocket with 400 plates, 400 gears / Working as expected

- Platform with 200 plates, 0 gears in cargo
Custom minimum payloads = 1000: Requests 1 rocket with 200 plates, 800 gears / Expected 2 rockets with 1000 plates, 1000 gears
Custom minimum payloads = 500: Requests 1 rocket with 200 plates, 800 gears / Expected 1 rocket with 500 plates, 500 gears
Custom minimum payloads = 200: Requests 1 rocket with 200 plates, 400 gears / Working as expected

- Platform with 400 plates, 0 gears in cargo
Custom minimum payloads = 1000: Requests 1 rocket with 1000 gears / Working as expected
Custom minimum payloads = 500: Requests 1 rocket with 1000 gears / Working as expected, as a single-item-payload, even with the lower custom value
Custom minimum payloads = 200: Requests 1 rocket with 400 gears / Working as expected

- Platform with 200 plates, 200 gears in cargo
Custom minimum payloads = 1000: Requests 1 rocket with 200 plates, 800 gears / Expected 2 rockets with 1000 plates, 1000 gears
Custom minimum payloads = 500: Requests 1 rocket with 200 plates, 800 gears / Expected 1 rocket with 500 plates, 500 gears
Custom minimum payloads = 200: Requests 1 rocket with 200 plates, 200 gears / Working as expected