x2Looks like the spacer is for use in a different after market application maybe a different version of the V6 TDI engine ?. I cant see any reason for it on your car but others may know better
this would be my guess as well
do you have the old tensioner? would be a quick measurement of the total stack height of the original one v your new one w/ and w/o the spacer to see which orientation is correct
edit - the shady russian parts catalog sites have been down for me the last couple days, otherwise id check the catalog and see if they show the spacer ...