Reply to "Wilton Meringue Powder - Recipe and Ratio Don't Match"

All I can surmise is that the royal icing won't set if you use the lower ratio they say works for "baking", because they are calling for a much higher concentration of meringue powder (and therefore egg white powder) in the royal icing recipe. Since the meringue powder has other stuff in it, in unknown quantities, it's not as easy to translate to egg white equivalents as is pure albumen. I'd either call them for more info, or use the recipe for royal icing as they wrote it, and then at the lower concentration, and see how the results differ in practice.