I meant the numbers you quoted. The site you link to does have some numbers on pretrial detention, and by the looks of it drug-related offenses there too are a minority of those jailed, but a sizable one. They're careful to list various caveats, so let's not overinterpret the numbers; there may be overlap or overcounting; and if you're trying to discern possession vs. other drug related offenses surely that's yet another wrinkle which a cursory skim doesn't answer anyhow.
Which two numbers? The only number I quoted is 20%, and that's for all drug inmates, not just possession. We don't have the numbers for possession, but they're surely much, much lower.