Modifying 'at risk'

I understand “at risk” to mean something like “having the possibility of danger”.

We measure possibility by probability, which ranges through impossible (zero), low (near zero), intermediate, high (near 1) or certain (1). From that standpoint it makes sense and is linguistically communicative to use the phrases such as “at high risk” or “at low risk”.

At my age I am at low risk of dying from a mountaineering accident (I don’t go on the mountains now) but at high risk of dying within the next two decades.

If your question is about the use "high at risk" or "at risk high", I have never encountered such phrases. The first has no meaning unless in modified usage such as "they stood, highly at risk, next to a tiger". The second has no meaning unless modified in clauses such as "They are at risk, high because they stand next to a tiger".