Definition of an internal reference

Warning: extreme pedantry.
I am performing [Gutmann-Beckett experiments](https://en.wikipedia.org/wiki/Gutmann%E2%80%93Beckett_method), basically utilizing an NMR-tube with my sample and a 31P-lewis base (e.g. triethylphosphine oxide) inside another one with a standard/reference (e.g. trimethylphosphate). This is classified as an internal reference, but I am unsure about that. Wouldn't an internal reference be in direct contact with the sampled solution?


Since we need a constant 31P signal to reference, I understand that the reference has to be isolated, and wether this is "physically" by glassware or by an extensive shielding residue is irrelevant (when the signal is constant); but somehow this is not what I would call an internal reference.


