I won't say sweet 16, which is the most stereotypical floor to declare.
BTW I wouldn't ever call S16 a "floor".
As I said, for Purdue, making the tournament is the expectation--i.e. the floor. It is what defines a minimally acceptable season. Fail to do that one year and questions start getting asked. Fail to do that two consecutive years and your seat is going to be toasty, and you may not be allowed to sit in it.
It also bakes in some assumptions. While Purdue being in the B1G regular season championship hunt is important, trying to get the BTT double bye is important, and trying to win the BTT is important, if they succeed in any of those three things they're making the tournament. So making the tournament is a good proxy for the regular season having gone acceptably well.
Now, if they were several games out of the B1G regular season hunt, don't win the BTT, and get into the tournament is a 5-11 seed because it's a bit of a "down year"? Now, getting to the second weekend is overperforming. And if that's the case, then getting to the second weekend turns a "meh" but acceptable season into a "good" season.
Likewise, if they're right in the hunt and either win the B1G regular season and/or BTT, they're going to be a top 4 seed. At that point,
not getting to the second weekend is underperforming and turns a good season into "meh" but acceptable, but getting to the second weekend means that even if they don't go farther, it was still a pretty "good" season overall. They maybe get to hang a B1G banner even if they can't hang a Final Four banner.
So that's why I said a S16 is the metric for a "good" season... NOT that it's the "floor".