I seem to recall this has been discussed before... A little searching might give you more information.
As you can probably gather from the comments above, the answer boils down to what kind of lighting you hope to achieve.
The "general wisdom" for beauty dishes is that they work best one to two times the diameter distance from your subject. By this rule of thumb, your 16" dish would be optimal at a distance from 16-32" from your subject. As the size gets larger, not only do you gain the greater spread from the larger diameter, you also gain a greater spread from the greater distance. So a 22" dish can be used from 22" to 44" away. Get to a 27" dish and you are backing up between 27" and 54"!
What I just wrote is all theoretical. In the real world, there are a few other factors. Beauty dishes are made differently, so there can be significant differences between designs. More importantly than that, what your taste is in how you want the light to look and what mine is are potentially very different. Not everyone uses the above rule of thumb.
What most of us do is try the modifier, look at the pictures, make some changes, look at those pictures and, over time, decide what look we want in a situation and pick the tool, position and angle accordingly.
In short, I think everyone is trying to be helpful, but it is a hard question to answer well.