Looks like no one has commented so I will.
'my guess' is that both engines would use a top ring of the same thickness.
Obviously yours are different.
And 'tight' isn't necessarily the spec.
Get the spec, in thousandth's of inches out of Bentley, and measure it with
a feeler gauge.

A company that I like, for Rings, and that's all the do, piston rings, is
Deves.
They'd have the spec for thickness of the top ring for each engine.
Perhaps the very loose top ring in the 2.1 isn't really a top ring, but a #
2 ring  - that could account for the situation you are having  - if someone
changed rings, I would sure consider this possibility. 
But get the spec, measure it with a feeler gauge.
If you wanted to buy good used matching pistons & barrels, for either 1.9 (
why even bother with one of those is where I'm at these days ) or 2.1
......I have them.   Compete set of four would be harder,  but I do have all
this stuff, good used.

Scott
www.turbovans.com 

-----Original Message-----
From: Vanagon Mailing List [mailto:vanagon@gerry.vanagon.com] On Behalf Of
Giasson, Pascal (DNR/MRN)
Sent: Friday, July 27, 2007 4:28 AM
To: vanagon@GERRY.VANAGON.COM
Subject: 1.9 vs. 2.1 top piston ring width

Does anyone know if the width of the top piston ring on 2.1 are wider
than the 1.9's.  The top rings on my 2.1 are looser in their lands than
the ones on my 1.9, yet if I take the top ring from the 2.1 and put it
in my 1.9 piston it is tight like it should be.  The PO of my 2.1 said
he put new ring on it and I'm wondering if he got the wrong ones or if
the pistons are worn out.  Thanks 

Pascal