I have the same problem, and I have a Phil Wood crank bearing and a crank with a fair reputation.
My lbs says he sees this problem to some degree with almost all bikes.
Some of it comes from a slightly out of round crank; some of it from an out of round chainring; some of it from a bent crank spindle; and some of it from an out of alignment bottom bracket.
Sheldon Brown has a good chainring centering technique that often makes the whole assemblage act round.
With the chain on and reasonably tight, but with the chainring bolts almost loose, slowly rotate the crank.
When the chain gets tight, hit the top of the chain at the middle of its span with a heavy wrench or a hammer handle.
This will move the chainring in a direction that will loosen the chain at its tightest position, but may tighten it up somewhere else in its rotation.
Keep slowly rotating the crank and hitting the chain at the tight spots, but not so hard, until the chainring has centered on the crank.
During this process, slowly tighten the chainring bolts.
The above has worked for me with some cranks.
However, with my present crank and bottom bracket, and all of my chainrings (I have more than a few), the chain tightens at the one o'clock position no matter how persistently I use Sheldon Brown's method.
Hm.
I can't move the chainwheel far enough to get it centered.
However, I have discovered that if I flip the chainwheel around, so that the countersink bevels for the chainwheel bolt heads rest inboard against the star of the crank, this gives me more play and adjustment for centering the chainwheel, and Sheldon's method works perfectly.
This has given me a cheap fix for this crank, crank bearing and bottom bracket setup, which I otherwise like very much.
I suppose it might look a little weird, since the chainring bolt heads do not recess into the chainring, but I've gotten used to it.
I now have a perfect chain, with constant tension for the whole 360 degrees of crank rotation.