Consider using -n 1000 to get a better idea, but be warned that this will take a fairly long time if you're scanning multiple plots.
For more detail, you can read about the DiskProver commands in chiapos
What does the ratio of full proofs vs expected proofs mean?
If the ratio is >1, your plot was relatively lucky for this run of challenges.
If the ratio is <1, your plot was relatively unlucky.
This shouldn't really concern you unless your ratio is <0.70
In theory, a plot with a ratio >> 1 would be more likely to win challenges on the blockchain. Likewise, a plot with a ratio << 1 would be less likely to win. However, in practice, this isn't actually going to be noticeable. "Number of plots" and "k-size" are much more influential factors at winning blocks than "proofs produced per challenge". Therefore, don't worry if your plot check ratios are less than 1, unless they're significantly less than 1.