GetScaledCapsuleHalfHeight multiplies the CapsuleHalfHeight by the lower scale value, even if it is X or Y. Seeing as Half Height should only be related to the Z scale, this does not work out properly if the X or Y scales are lower than the Z, returning lower values than expected.
Regression?: No
This occurred in 4.18
There's no existing public thread on this issue, so head over to Questions & Answers just mention UE-59651 in the post.