http://www.youtube.com/watch?v=O2nu8C7dIQg

Your suit's precision should have to beat their suit's profile for this to happen. Had posted this in the past but I figure it needs to be brought back up.

Last time I checked, hiding behind a hill masks your profile from the enemy precision scan. This video just confirms my theory.

Also, the built-in base precision of your suit is only meant to pick up most medium and heavy frames. They were never meant to pick up light frames like the scouts. You can try to augment the precision scan to get maybe a scout with a standard profile level, but you're never gonna be able to track a proto scout. Nothing wrong with that.

EDIT:

If you're talking about being spotted beyond the 10m range, he was within your line of sight which means he will light up regardless on the mini map. By the way, the passive scan range for scouts has been recently buffed to 16m now.

Then you're doing something wrong. If he's hiding behind a hill, that might explain why. But if he's hiding behind a man-made wall, then it's pretty obvious he did everything he can to reduce his profile. But even then, a fatty shouldn't be able to hide from me. What is your current fitting?

That explained it then.