which sculpture artist is mainly associated with the 4th cannon of proportions?

Answer 1

There is no 4th cannon of proportions.The ancient Greek sculptor Polykleitos (active ca. 450-420)clitus did make a list of these rules, but all but three are lost.
Everything u might want to know about the subject is, l think, written about in the two links below:
http://vrd.askvrd.org/default.aspx?id=12488&cat=1473
http://www.atrium-media.com/rogueclassicism/2004/09/02.html
scroll down to the paragraph in blue titled: Golden Mean and Olympian Form

Answer 2

4th canon
but which one, there seem to be many.