Adam, in this particular case the Pooleys mock exam might not be entirely representative of the CAA exams. If there would be a CAA exam which had choices 44 and 46, and an actual measurement would yield 45, then there'd be too many complaints from examiners and candidates, and the exam would've been changed long ago.
Pooleys doesn't have such a direct feedback mechanism so questions like this may stay in their books for years.
So I wouldn't worry about this. As long as you can do all the calculations properly based on a best-effort measurement, and are consistently within one or two degrees of what Pooleys considers the proper answer, then you're going to be fine.