Large ships being more detectable makes sense. There's already a mechanic making it harder to jam/cloak large ships however. If you're running a small jump shuttle, then I can see it being harder to detect/identify an object. There could a range at which an object can be detected, and another range when your scanners can detect what it is that's floating out in space. Until it reaches the indemnify range, your radar only sees it as being an anomaly.
Of course, this would also make the astronaut very hard to detect at range, which I like a lot. If you've lost your ship and are limping through space, then you have enough to worry about besides being blasted by someone or a pirate... 2000m range for detecting an astronaut seems good enough, assuming they're not firing a weapon or something. Firing weapons should increase your detection radius considerably.