I think that mustard has a lot of acid in it. The acid is used to inhibit the enzyme that produces "hot" compounds in the mustard. When you neutralize the acid(s), you will be making salts. At some level, you may not care for the taste these salts give. Two other possibilities come to me in this case, first a blend of prepared mustard with baking soda augmented with some dried mustard powder and / or seed could work. Another option would be to go with all mustard powder and seed, in which case I would lower the amount to control the heat. Let us know how you do with whatever way you choose as it may help others.
Fashionably late will be stylishly hungry.