If you mean POIs that leave a blue circle on the Ship Scanner - those will be slightly visible anytime the Ship is >1.5km Altitude and fully visible >2.0km Altitude (AGL = Altitude Above Ground).
Just ensure the Scanner Range is set to maximum, otherwise it's easily possible to miss them.
Keep in mind, though, that several of the typical minor POI you can encounter in the SRV will not create a blue circle on the Ship Scanner and hence will not be detectable that way.
In order not to miss these, good old visual lookout is still required.
PS.
If you're looking for scoopable Cargo POIs, there an old trick that should still work if you want to locate it within a large blue POI circle on the Scanner (since the actual POI location is typically not in its center and must normally be located from the SRV) :
- Equip a 1B Collector Limpet Controller (1400m Range)
- Launch a Collector and lock it up as a Target from the Contacts Panel
- descend within the deployed Collector Limpet to a lower Altitude within the blue circle (below 1km or less)
Should the Collector detect anything scoopable within its 1.4km Range, it'll start heading towards it immediately until it crashes right into it and expires.
Turn the Ship to follow the Collector Limpet - and you have your precise POI location.