This is an excerpt from the Azure IR documentation:

For copy activity, a best effort is made to automatically detect your sink data store’s location, then use the IR in either the same region, if available, or the closest one in the same geography, otherwise; if the sink data store’s region is not detectable, the IR in the instance’s region is used instead.

I want to ask if the sink location is not detectable, then instead of falling back to adf’s location shouldn’t source location be considered? Also, is there any reason that sink location is considered instead of source?