Read the primary source rather than the write-up and the two do not agree, so here is what is actually in it.
The variables that decide how a cross-border order goes are declaration wording, the destination country's import rules for prescription medicines, and whether the shipment looks commercial. Personal-import allowances exist in some jurisdictions and not in others, and where they exist they are usually conditional on a prescription and a quantity limit. The failure mode is normally a seizure notice rather than anything worse, and a reshipment policy is the thing worth confirming before ordering rather than after.
Where I think it is weakest: the population was selected and supported in ways a real cohort is not, so I would read the effect size as a ceiling rather than an expectation.
What I am after is which of the variables in a cross-border order actually determine the outcome, and which are superstition. Practical detail welcome, however dull — the duller the better.
Note on sourcing:
Figures above are from the primary publication rather than the press summary. If a number here disagrees with one you have, post yours and we will work out which of us is reading a secondary source.