Top Radiator Hose Collapses

1972 Duster Top radiator hose collapses after engine cools down, I have read and read about why and have look at many of pages on why this happens but after replacing the Cap with a vented and non vented one it still does it to the top hose. I don't have a reserve system just a chrome catch bottle system. The car does not run hot or over heat it run 190 maybe plus or minus a few but over all wise it run good. There is no coolant in the catch can nor is it over filled. From what I can tell about being over filled. When its cool the lever is down about 1/2 inch from top. So I am not sure what is going on here. I am not sure that this is causing any trouble except for wearing out the hose but if I open the cap while cooled it will fix the hose to the proper shape.

Please let me know what could be the trouble.

And please don't tell me to put a reserved system in place of what I have now...

Thanks