So I was re reading your reply, and I did notice that there is never anything in the reservoir can. Makes me wonder if it's blocked and not allowing any fluids to come up through it and that's what's happening also
Does your radiator have the correct pressure cap rating, ie 15 or 16 pounds? I don't know what the factory spec is, but sometimes the wrong pressure cap, ie lower, will allow the antifreeze to escape at the lower pressure when it should actually be higher.
On my '73 Fury, using it as my example on how this works, I have a 16 pound cap. I filled it right to the top of the radiator, then put the cap on. I then put antifreeze into the overflow tank and filled it about mid-way between add line near the bottom and full (maybe it says "hot) line near the upper portion of the tank. When the engine gets warm/hot, the expanding antifreeze will exit out the cap overflow tube due to pressure, and travel through the hose connected to the overflow tank, and spill into the overflow tank. The line that goes into the tank must reach near the bottom of the overflow tank to work correctly (sometimes this tube falls off, deteriorates, or is flat out missing). Now, when the engine cools, the antifreeze cools, and the fluid contracts. The radiator/cooling system creates a "suction", and antifreeze is then pulled from the overflow tank, back through the hose in the overflow tank, back through the overflow tube at the radiator cap, and back through the radiator cap itself until the radiator is full again. So the radiator cap not only allows antifreeze to exit under pressure, it also allows antifreeze to be drawn back in under suction. If not, when things expanded, you would be blowing out cooling system parts, and when things cooled, you would be contracting cooling system parts and they would be collapsing.
Your radiator cap needs to be of the pressure-type radiator caps which contains a relief and vacuum valve. So make sure you have one of these for the proper operation of an overflow system. Make sure your overflow line is not collapse, cracked, or sucking air. The line must go near the bottom of the overflow tank and you want to have an angle cut on the bottom as a flat/straight cut hose can suck itself to the bottom of the overflow tank and not allow antifreeze back into the radiator.
I assume yours is similar to mine in operation, but maybe someone here can chime in and confirm this. I suspect a Service Manual for your car would show this.