This depends on the manufacturer. Let's say we have a Relajado Robusto and a Relajado Churchill and they are both Cameroon wrapped with the same binder and filler. The same exact tobacco is created to make both and both will have similar qualities, but size is going to have a major impact on the taste due to the fact that they will burn differently and their differing lengths and widths will create a different flavor and temperature for the smoke. It's not that one is better than the other; different smokes for different folks.
If everyone liked the same cigar, it would make the guys in the warehouse much happier. Some manufacturers will create different blends for each size in a series to facilitate the burning characteristics for each cigar to actually make the cigars more homogeneous throughout the line, but this is more often seen on ultra premium cigars. They are essentially changing the blend for each cigar to make them more alike throughout the line However, if we are out of your favorite smoke, the next size up (or down) is going to be as close as you can get to that blend and will have the same tobacco.