I hate the term 2-row, it's so vague. I have a brewing book dedicated entirely to Bavarian Helles and the author writes that 2-row barley malt is the malt that is used, when all the German breweries are using pilsner. I think
technically pilsner malt is made from 2-row barley, so he's not wrong, but it's still confusing as hell. Someone correct me if i'm the guy whose wrong
A batch with vienna would probably be a good idea.
Subtle tasting beers like kolsch are tough to nail down, it could likely be that their
balance of the ordinary, standard kolsch ingredients are in perfect harmony and it isn't a particular ingredient at all you're tasting. In beers like kolsch, the absence of certain additions might as well be their own flavors because the base malt, bittering hop and yeast all get to do more of the heavy lifting than say, an APA.
I'd recommend you try that formula, along with 10 or so other formulas over the next few months to get your recipe nailed down on your system. Can you post the base recipe and process of the kolsches you've been brewing? We may be able to find something missing in your recipe, or something there that could be masking the flavor you're looking for. I need to get out to BJ's and try it, there's one like 15 minutes way from my house. No excuse =[.