Blends and tasting balanced

How do tea companies get a blended tea to always taste the same. Say I bought a breakfast tea blend and it combined Assam, Ceylon and Kenyan teas, how do they make the blend of teas so that every time you make some it will taste the same. It has puzzled me for a while, the first scoop could have more Assam then the next scoop I go in for – is there a trick to this? I’m guessing using finer tea grades helps the balance?