Strange overflow bottle question

Had radiator, hoses, cap, thermostat replaced last year.
Been eyeballing level in overflow bottle past few months. Then it dawned on me the level does not go.up or down when the engine is hot. I.mean I open tje cap and the fluid that drips out of the hose is ice cold, and the radiator is hot.
When the engine cooled down i pulled off the radiator cao and it was full to.the top with fluid.
This makes no sense, physics says when the engine gets hot it expands, the fluid gets pushed into the over flow bottle, and when it cools down and contracts it will suck the coolant back into the radiator.
For the life of me i cant figure out why i drive s half hour to work, temp guage is right in the middle whete it should be, heater works fine, no coolant leaks, does not leak a drop of coolant. But why is my coolant bottle not moving up.or diwn and the fluid in tje bottle is ice cold? By all rights the coolant bottle should rise about an inch when the engine is hot. Any ideas? Is it due to the cold weather?