Detection times are determined when the shot or pill is taken.
But they mean different things for different drugs. In order to get your T/E ratios back in line then you will concern your self with half lives of the drug. But with orals the half life may be less than a day - but the metabolites could be in your system for months.
Also, the more you take the longer the drug can be detected. Along with alot of other facts - the detections times should be taken very lightly.
As far as avena sativa - I doubt it would effect t/e ratios at all - but I have not seen any studies on the subject.
Nautica