I did not intend that as an empirical observation but rather a mathematical pharmacokinetic result of fat-solubility rather than water-solubility. THC is fat-soluble and so has a higher volume of distribution which drives a longer half-life.

(See Shulgin “The Nature of Drugs” pg 132)

And “constant” would be a better word than “permanent”, as certainly it should go away after some weeks of abstinence.