Will a radiator overflow bottle automatically siphon back in when cold?

Does this help in anyway to keep the engine cooler than not haveing a recirculating cooling system?

Using a 7lb cap would allow more coolant to fill the bottle than a 16lb would be the only difference wouldn't it?

I had one on another car with a 16lb cap and I never saw any difference in the bottles coolant level.... it was always the same no matter if the engine was hot or cold.??? I have been working on getting the temperature down on my car and have been putting things together. One thing on the list was a recirculating cooling system but didn't know the proper cap to use.