Proportions and the charts simply don't work on these stones.
You need to test and look at them to see the light return.
Some with large tables and shallow crowns look good,but not all the time.
Rounds are fairly predictable using proportions to guess sight unseen.
The fancy shape stones cannot be judge by just the numbers. The stones must be seen.
Iknow this isn't what consumers want to hear, as they don't want to pay for more than one stone, or pay for more than one stone to get it checked. Consumers want to depend on charts and the "easy" stuff to make their decisions.
For rounds this works 70% predictable.... for fancy shapes its much more difficult. However, if you compare the merchandise quality offered on the net vs. the price you pay at a store, the savings would usually help to defray the examination costs of having more than one stone checked out.
It also dependson the quality and intensity that you want. Maybe you don't want the cat's meow of light return. Not everyone buys a Ferrari. Then again, maybe you want the Ferrari ???
Rockdoc