Which heavyweight fought least rounds per game?

[jiopsi]

Was it Tyson?

I have these

3.7 Mike Tyson (216/58)
4.1 Jack Dempsey (283/69)
4.1 Ernie Shavers (367/89) (non-champion)
4.2 Rid**** Bowe (195/46)
4.3 George Foreman (349/81)
4.9 Rocky Marciano (241/49)
4.9 Sonny Liston (267/54)
5.0 Vitali Klitschko (235/47)
5.1 Wladimir Klitschko (334/66)
5.1 Lennox Lewis (225/44)
5.4 Max Baer (423/79)
5.8 Joe Frazier (213/37)
6.0 Joe Louis (417/69)
7.6 Evander Holyfield (443/58)
8.9 Muhammad Ali (548/61)

[BattlingNelson]

Butterbean 261/91. 2.8
Lamar Clark 90/46. 1.95

[jiopsi]

Forgot about Butterbean. Well not really in same category but at least he's known from that. Clark I believe fought even non-boxers and so, so it really isn't the same.

What about fewest rounds of hw champions?