And that's assuming they wanted to place him centrally of course. Considering we haven't the faintest idea what the monument was for that's a pretty unjustified assumption for us to make.
Not implying a connection but I think the King's Chamber of the Great Pyramid is also off-centre, though I seem to remember reading somewhere that it might be a decoy or 'failed structure' and there might be another chamber in there somewhere.Seems hard to imagine that the builders/designers of Silbury weren't tempted to build a chamber within their amazing structure (or is that time capsule mentality creeping in :-) Would imagine that if a chamber was constructed it would have been located nearer the top (less weight). Folks already had the expertise to build stone burial chambers and then cover them with earth - can't really see why the same technique couldn't have been employed on a flat, unfinished level of Silbury and then the rest of structure built around it (think that's what was done at the Great Pyramid).
One problem - wouldn't such a chamber show up on the sonic tests that have recently been conducted at Silbury?