I was only using online sources (and I checked several for corroboration) but I agree the direction of your measurement of the mass of one tsp of Na2CO3 even though I measured 53grains/15.4grain/gram = 3.44grams of Na2CO3 per teaspoon instead of your 2.3grams. I see in the Wikipedia data on Na2CO3 that the density changes dramatically whether it is anhydrous or not.....
So I am confused. I wonder if the baked anhydrous is becoming "hydrous?"
I put 12.5grams of baked Na2CO3 in 2 oz of water for a 2molar solution (2 x 106gram x 2/33.8 = 12.5gram) which I used 1/2mL (12 drops applied to a Liter, out of a measured 24drops per gram of H2O).
Using a reloading powder scale (1gram = 15.4grain, and 0.1grain resolution) is, I hope, much "more better" than using a volumetric level teaspoon or level tablespoon measure and questionable online conversions, as I was doing before last night.
rogwhat53