Crossword Genius

Lukewarm self-assessment? If so, there's no getting over it (10)

Ross

I believe the answer is:

impassable

'if so there's no getting over it' is the definition.
(something impassable cannot be travelled over)

I cannot understand how the remainder of the clue works.

(Other definitions for impassable that I've seen before include "Blocked to travel" , "preventing progress" , "won't be crossed" .)

I've seen this clue in The Times.
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