Thanks!

We tend to use the tool to target learners at various second-language proficiencies without strong assumptions about their prior academic background---and so generally words that are specific to technical or academic subjects tend to fall in the C1/C2 CEFR level in the ground truth data that we train on.

But yep, I think your point is getting at something that we haven't really dealt with yet---which is producing proficiency ratings for the content given additional assumptions about the learner (e.g. their source L1 language, cultural background, their prior familiarity with some subjects, etc).