My husband received the US Centurion invitation on Monday yesterday. It's been years since we joined the forum and this particular thread helped us alot with insights of Centurion etc.
So I think its time to contribute here based on our own experience.

Background:
We are purely based in London, UK. My husband had the first UK Amex Plat since 2008.
Our UK spending are around £6-10 million per year from 2015, 70% on business plat, 30% on personal plat.
My husband made a global transfer from UK to US back in early 2017 for the US personal plat. Since the card was opened, he made 0 spending on the US plat. Yes, we missed the card opening bonus because my husband literally just wanted a US plat for backup use when he traveled to US (UK amex has 3% FTF). I didn't ask why he didn't make any purchase by using the US plat.
By mid of 2020, we spoke to UK centurion team and tried to see if they could possibly offer an invitation, but failed. So my husband decided to move some of our personal spending to his US plat and see if he could secure an invitation.
He applied to get Gold, Green, Marriott, 3 Hilton cards within 6 months from June 2020 as he planned to close all UK amex personal cards once the US amex portfolio is ready. By then he spent minimal on all those US cards just to get the opening bonus.
We actually started to use the US personal plat since March 2021. We had the spending amount as per below.
Plat: $1.2 mil
Gold: $500k
Marriott: $150k
We don't spend anything on the other cards. These are all personal spending. Mainly luxury shoppings and high end restaurants etc. We didn't move biz spend over to the US cards yet.
We had been thru 2 FRs since March this year and my husband was quite familiar with the process coz we already had countless FRs in UK since 2015.
I would say our point & mile portolio is good. My husband have 6 million membership rewards in the UK account. 13 million Marriott Bonvoy points, 3 million Hilton Honours points and 2.5 million avios in the household account.
Because we have a nice points portfolio, we had minimal luxury travel spends on our Amex cards. We used points & miles to redeem our travel 100% of time.

Just to give you a rough idea how my husband got the Cent invitation less than a year which really surprised me tbh, compared to our 5 years' spending history with UK amex.
I think there is one thing worth pointing out. In mid of September this year, we called up Plat helpline to see if they can try to arrange the invitaton (you don't try you never know). The lady on the phone was very nice chatting and she said she can put my husband through to the Centurion team. Then he waited for 20 mins and was passed through to the Centurion customer service. Another lady on the phone said he had gone through my husband's profile and she thinks its good for a review. She told us she would send over to the Cent review team and would definitely have a call back to us from the team within 2 weeks. My husband asked twice, if he was not qualified for the Cent review, will he still receive callback? The lady said yes, they will definitely call us no matter the outcome. I was abit surprised coz normally there shouldn't any callback if the invitation is not secured.
And yesterday afternoon my husband received a call from Cent team to be offered the black card. The process took about 30 mins for t&c etc. We can see the package is on the way to our US home now.
Also, in the past 6 months my husband registered his interest on the centurion.com quite a few times as per those bloggers mentioned on the internet, we both don't think it helps. I think its better to call up the cent helpline and try to request a review if you are confident with your spending.
Regarding the postcode/area, we don't think it matters. Our US address is near Seal Beach, Los Angeles, but all our spending is in Central London and Europe when travelling. We had 0 spend in US since we had those cards.

I hope our experience to secure the invitation can give a bit of help here and thank you so much for the insights all these years.
No matter we are just lucky or not, I would say this thread is most useful on the internet with regard to Amex centurion card.
Thank you everyone.