Center isn't very important as the POI likely isn't going to be there.
I could almost argue it's almost better to land at the edge and make a zig zag sweep forward (Remember you seem to always exit your ship with the SRV facing backwards, so remember to turn around as you exit, if you landed with the nose pointing towards the center).
I also usually climb to above 1.5km and keep the scanner at maximum range (zoomed out) so I don't miss any blue circle appearing. As you approach it, it seems to deform into some elliptical blob, probably due to the scanner logarithmic scaling I have, but it doesn't matter that much.
Also, when you drop below 1.5km, the circle vanishes anyway so make sure you make a slow but vertical descent.
I'm used to smaller moons with 0.05G and such and I just "landed" on a 1.5G planet. Quite a difference!!! Good thing I got shields...
I rarely hear the sound of the POI when I start with my SRV. I have to find those scanner blips that are more towards the upper part of the scanner. Also, when I do start to hear it, it sounds like when you're looking at your own ship.
If you leave your ship on the ground, drive a bit away from it and turn towards it and listen to the sound. That's usually what artificial scanner blips sound like, in my experience.
There's a post containing some scanner echoes and sounds somewhere in this forum...