I have  a question about the the off target region.

 suppose the locus is 1000 for a target frame of 20bp in the sequence.

Now what will be the region of consideration for the off target analysis.

What i understood from papers and links, that  it should be plus/minus 500bp from target region at max.

Shall I consider the  the locus from 500bp to 1500bp to find out all potential of target for the target frame at location 1000.

If I am wrong please guide me.