Example, i have a huge wheat farm, but my production is terribly slow, because of the Portable Storage Interface only sending 1 stack of wheat at a time (with a Brass Funnel). So, add the option to wrench the interfaces, like how many items it transfers, at what pace, and way more. (It's the creators' decision after all.)

If you increase the speed of the output, in your case probably a belt, it should be a lot faster and wait until the inventory empties.

No, that's not the case. The wheat farm in case is very slow to connect to the interface. It takes almost 1 minute to reach again the other interface. Increasing the pace of how many stacks at a time would be very useful, as the production would fill an entire chest with wheat instantly instead of having to wait a minute for a stack.

In your case the problem is most likely the inactivity timer built into the storage interface. If items are not pulled out of it frequently enough it allows the contraption to move again. Make sure that the speed of your output belt is at least 28 rpm. That way it will pull out another stack before the inactivity timer gets triggered and the contraption starts moving again

We've just encountered the issue with the inactivity timer too in a 1.16.5 pack, would be nice if it were configurable with a wrench or something, or if it worked at say 16RPM which feels like a pretty standard "low-end" belt&chute extraction speed without being too slow.

Thanks for mentioning the timer by the way, it was driving us mad trying to figure out why our interface would only connect, send like 1 stack, then disconnect with the contraption's storage still nearly full.