Hi there! Thanks for using the mod!
You're correct, the ammo loader waits until it has a minimum of 10 of an item before it starts loading entities. This is because the script logic to add/remove entities as consumers is quite expensive, and is even more so if it is upgrading ammo/fuel. In my tests, doing this while the chest only has 1 or 2 items leads to quickly escalating UPS costs as the chest constantly has to register and then remove itself as a provider of that ammo/fuel.
If you'd like, I could probably make this a mod option so you can decide for yourself if the UPS hit is worth the quicker response.