The way that feature works is the autominers fill up as normal and then once it’s full the overflow is transfered to your OCD.
For example,
Let’s say you have a L10 gold autominer. Once it’s completely full then you will start to see 33 gold added to your OCD per hour. The autominer will stay full and only the overflow gets transferred.
Hope that helps.
Welcome to HWS. I hope you enjoy your time here.