Inconsistent input buffer sizes

Input buffer sizes on Assemblies and other machines seem to follow the following general guideline:

Truck import ON: 4 batches (at least 40)
Truck import OFF: 1 batch

However, there are quite a few exceptions to these rules, without an apparent pattern afaik. (See images for examples)

From my pov it would be nice if these inconsistencies could be ironed out, as it throws off the feeding balance on some of my advanced builds.

When connected to belt, the buffer stores at least amount needed to run next product creation.
The calculation I do not know, but the size in most cases is calculated as 2 multiplied by input count.
In case you have more recipes with same input product, I thing, it would take always the biggest one.

I think that last sentence there was the clue that I was looking for