I'm using this website for data.
There have been three sub-40 RPI teams to host since 1999 (current format), all gifted to northern schools.
year - RPI - team
2000 - 42 - Minnesota
2001 - 62 - Ohio State
2002 - 44 - Notre Dame
None of those were the #1 seed, and none of them won their regional. In fact, we were the #1 seed at the 2001 Ohio State regional, which we won.
There have only been six hosts who had an RPI outside of the top 32 (out of 224 regionals in that time).
87% of teams with RPI in top 12 have hosted.
77% of teams with RPI in top 16 have hosted.
And this has gotten better for top teams in the last 6 years:
93% of teams with RPI in top 12 have hosted.
83% of teams with RPI in top 16 have hosted.