Yea, the HCA is only the basic guide to check the proportions but is only the first filter you should use. It's a useful guide but not 100% reliable. It has many limitations on it and alot of other bros here said, you need to use it with the ASET and Hearts/Arrows scope too. If not it'll just mislead you to end up buying a bad diamond.
From what I see on your GIA cert:
1. It's a 60/60 diamond. Your table is 60 and depth is 59.9. 60 Table is wider than the recommended range and when combined with a shallow depth close to 60, it can end up as a bad combo. Garry Holloway (the creator of HCA) advises to be cautious abt it too.
https://www.hollowaydiamonds.com.au/60-depth-and-60-table/
2. The crown is on the shallow side at 32.5. The recommended is minimum 33. Too shallow crowns will have less fire = less sparkles.
3. The start length is 45% which is very small (HCA does not account for star length). I wouldn't go for anything less than 50% star length. The smaller the star length = smaller fire/sparkle
https://www.prosumerdiamonds.com/star-facet/
4. Your clarity is a VS2 and the only inclusion is a feather. Feather is a ''crack'' in a diamond. It's ok as long as its not visible and internal. But VS1-VS2 clarity grades with feathers are notorious for being on the girdles / surface. So I would double check to ensure that the feather is not exposed.. the diamond can get chipped if that's the case.
I'm not a fan of this piece as there are some inherent concerns which won't show on the HCA.
You can read:
https://www.jannpaul.com/content/holloway-cut-advisor-calculator-tool
HCA limitations
- The HCA tool ignores a diamond’s optical symmetry.
- It only takes into accounts 17 out of a diamonds 57 facets. Thus, it only measures 30% of a diamond’s facets!
- The 17 facets that it uses are only average values obtained from the certificate usually.
- It does not take into account extreme angles where it favors shallow angles diamonds.
- It does not detect painted or dugged-out girdles
- The HCA tool is only a prediction tool and it does not provide a live analysis of the actual diamond.
- A diamond with a low HCA score does not guarantee a high performing diamond.