Target Lock Distance

Forgive me if this has been gone over before, I have been unable to locate a mention. In the daytime, through the periscope, I can lock onto a target at approx 8500m. (m?) In the nightime, this falls to approx 5000. What file controls that distance? Tweaking sensor cfg. files seems not to effect this, at least not submerged and using attack periscope.

Are these distances adjustable, and if so, in what file?

I would be grateful for any info.

Thanks,

Bam