The only things I can think of why it doesn't scan for the range you set are:
(1) The scan will find the closest items that start with "SF " up to a maximum of 32 so if you have lots of objects called "SF something" close by that could be the issue. You can test by putting the scarecrow in an empty place and then try.
(2) The scan will only find objects that are in the same region, so if on the edge, for instance, it won't see anything in the next region even if really close.

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