Just had a look at what PWS's I have got fitted, either C or D rated, I don't have trouble finding Cores
But you would have even more the longer the range...with lower range you "DO" risk missing a core highlight that you can fly right past when you could be getting even more... but you won't actually know because you can fly right past them because the PWA won't display them as you spin the camera around the ship on external view from the pulse... thats the issue, ignorance of what you missed compared to another player with grade A...
You may be happy with it but that does not change you might have boosted pass other cores...
There could be another core right next to the core you mined, just out of the range thats is the risk people take...
it's even more luck when you reduce the range and then boost in a single direction on if the PWA will find a high price core...
For OP
The core mining is luck based RNG still... Were you drop in the ring hot spot to start with you could flnd more high price item cores if you fly in a different direction from your drop point than you did last time, you also could end up with 9 booby prize core rocks and 1 good rock out of 10...
Untill you set a prefixed course and then run it every 6 days you will be stuck with RNG...
Mapped core mining can be done if you have a fixed reference point and stick to it this then removes RNG as the next time you drop you know exactly how many cores were at the centre 0KM and on a direct line to the planet centre you then know exactly how many that flight line ended up with ... And if its bad you know not to go that way...
Pick your start point and stick to an end point and fly the path... Then next run change the end point in the same ring, say a nebula not the planet and do that direction run...
For fast core mining detection, Boost speed is more important than cargo rack or hardpoints...