If you want to maximize your potential returns, scan the asteroids with the highest gravity - specifically, from what I've seen, asteroids that don't require LG infrastructure tend to be more likely to have minerals, and if they have minerals, they're more likely to have (very) high concentrations.
Hmm...this is intriguing. Now I'm going to have to do some correlation testing.
Then again, my primary use for asteroids is orbital mining, and that requires small asteroids.
Still, it would be interesting to find an optimizable survey pattern.
Higher mass means the RNG is weighted towards larger deposits, but lower accessibility. Lower mass means the opposite. This is why super-terrestrial worlds tends to have huge deposits but often minimal accessibility, whereas asteroids usually have very high accessibility, but small deposits. Higher mass asteroids will still tend to still have higher accessibilities, but a better chance of a larger deposit.
Systems with younger stars are weighted toward a higher chance of deposits being present.