My question is: Most of my recipes that call for baking soda and baking powder (within the same recipe) call for more powder than soda. So I thoug...

Hello, Le Bec Fin (from the restaurant in Philly?), and thank you for this link to a most interesting article. No, I am not familiar with Kenji Alt Lopez, but I am definitely familiar with SeriousEats. Although much of the information in the article's "Leavening" section is exactly what I read on Wiki, it was the link at the end of that section that brought the best info, at The Food Lab: Baking Powder vs. Baking Soda | Serious Eats that more directly and thoroughly addresses the reaction with buttermilk:

A pancake experiment is described, where 5 batches of pancakes are made using the same ingredient amounts in each, BUT "with varying amounts of baking soda, starting with none, and increasing in 1/8th teaspoon increments up to a full half teaspoon." The 5th batch, with the full 1/2 tsp of baking soda "browned far too quickly, lending it an acrid burnt flavor tinged with the soapy chemical aftertaste of unneutralized baking soda. Interestingly enough, this pancake was also flat (my bold and underline) and dense—the inordinate amount of baking soda reacts too violently when mixed into the batter." So maybe this is a partial answer to why my muffins, with more b. powder than soda, rose higher and were fluffier.

I also noted this point in the first article: "I found that baking powder generally produces cakier cookies that rise higher during baking, producing smoother, shinier tops, while soda yields cookies that are craggier and denser in texture."

lalf, this is related to your question-- do you know the work of Kenji Alt Lopez at The Food Lab and Serious Eats? I just read a very long piece he did on ch chip cookies and all the components and their "purpose in life", incl bak soda and powder. Now, if this info could just FINally take root in my brain...!:
http://sweets.seriouseats.com/2013/12/the-food-lab-the-best-chocolate-chip-cookies.html

Hi susan g, thank you for the article reference, but also pls see my reply to Rochelle, under the "Comments" section for the recipe. BTW, just to add, my muffins exhibited no soapy or bitter flavor from too much b. soda or powder.

This article about cocoa also has details of the relationship between acidity and the use of baking powder and baking soda, and might help you. (And has more than I knew about cocoa too.)
http://www.kingarthurflour.com/blog/2014/01/10/the-a-b-cs-of-cocoa/?go=EP140110D&utm_source=EP140110&utm_medium=email&utm_content=&spMailingID=5998964&spUserID=NDYxNDczMzg4MjMS1&spJobID=360785406&spReportId=MzYwNzg1NDA2S0

Both Baking powder and baking soda are not at all uncommon in recipes. Baking soda is called for when the recipe contains an acid that needs to be neutralized. Baking powder consists of baking soda and two acids, one of which is activated (begins producing carbon dioxide, in other words) by water and the other by heat. If a recipe contains an acid, baking soda in a ratio of 1/2 teaspoon for every 8 ounces of acidic component is added in order to neutralize the acid, creating again carbon dioxide. If baking soda were not added, the baking soda in the baking powder would be siphoned off by the acids, depriving the formula of its inherent leavening properties. I agree that the baking soda seems high at 2 teaspoons, inasmuch as 16 ounces of buttermilk would necessitate 1 teaspoon. Blueberries fall in the middle of the acidic end of the pH scale at 3.1 - 3.4, and they are left whole, so they really don't contribute significantly to the acidic components of the recipe. I like more rounded muffins, too, and I think you'd be fine using a full teaspoon of baking powder and 2 teaspoons of baking soda for a full recipe. And if you use dried fruits, be sure to hydrate them in hot water for 15 minutes before draining them and proceeding to mix.

Thanks, Chris, for your speedy answer! One thing, though, I don't want totally flat muffins (like those in the photos), which often results in using too little baking powder in a recipe with other rather 'weighty' ingredients. Any further inputs?

I agree that the ratio looks different from some, but the key here may be the two cups of buttermilk, which makes the batter more acidic. One rule of thumb I've heard is that for every cup of buttermilk in a recipe, you can use 2 teaspoons less baking powder and 1/2 teaspoon more baking soda.