It sounds like you may be talking about two different things. The first thing is that you can take multiple hits within an hour or so and the effects will stack as far as the size of your dose. This is just because that's how long the salvia stays in your system, it's not actually reverse tolerance.

Reverse tolerance is when, over weeks/months of repeated salvia use, you might start needing smaller doses to achieve the same levels on the 6-level experience scale. This can happen, and has happened to me, but it's not guaranteed to happen to everyone, and it can be pretty subtle even if it does. That's why there are a lot of different answers, because it varies from person to person.