From Labcoatian, and also supported by the relationship description:
Mirrors, while sharing the same ego elements, hold quite different standards for those elements. Each holds their base function to be something applicable to anything at any time, but holds their creative function to a higher standard, expecting anything done with it to be done well. Thus, mirrors will get into disagreements, with each partner trying to hold the other's base function to their standard of perfection, while at the same time trying to get the other to accept free and constant use of their own base function.