I think some of that will depend on the ratio... if it is square vs long... older cut or modern cut, four pavillion mains vs 8 pavillion mains... I''m confident that sweet spot standards CAN be had, but no one is researching it right now so it''s kinda a crapshoot.
The numbers you want for a cushion cut have NOT been standardized.
If you search PS you''ll find 60% to 65% for table and depth is one idea. Others say to just go with what looks good to you. Cushions can look very different from each other. Many people here will tell you that you really have to see them to decide.
I am using the 60-65 rule to get rid of clear dogs but going a bit outside it for ones I like.