CU6 has a $700m+ m/cap @edgescape but I reckon they look at the free float when screening for index eligibility, so they deduct the insider (Board, Executives, Founders) holdings and the Insto holdings, so that would include:

1. Dr Chris Roberts (NED), the former Cochlear CEO, through his company Cabbit Pty Ltd, holds almost 18m shares, or 6.84% of CU6;
2. Dr Alan Taylor (Executive Chairman), through his Family Trust (ACN 136 437 913) and his wife Sally Taylor, jointly control just over 14m shares, or around 5.4% of CU6;
3. Colin Biggin, Clarity's CEO & MD, 1.8m shares, or around 0.7%;
4. Charlie Morgan, through his own shares (in his name) and through TM Ventures (which he controls), held 7.18%, but is no longer a "Sub" (below 5% now);
5. Hong Kong’s China Grand Pharmaceuticals and Healthcare (China Grand) held options that would give them 8.3% of CU6 if those options were exercised according to this article: Clarity Pharmaceuticals to hit ASX in August (afr.com) [21-July-2021]; and
6. KKR-backed cancer care provider GenesisCare, held around 4% of CU6 at IPO.

That adds up to around 32.4%, although some of that has changed hands now (including at least 2.2% of the 7.18% that Charlie Morgan/TM Ventures held as he's below 5% now).

S&P may also be concerned about the outstanding options, including a fair chunk of options that the Board and Management hold, so if all of those were exercised that may well increase the insiders' hold on the company even further.

My understanding is that inclusion in the S&P/ASX indices is based on the free float (shares available to be traded) rather than the market cap, as I commented on in relation to GNG & LYL here at the end of my straw about DVP's inclusion: https://strawman.com/reports/DVP/Bear77?view-straw=25512.

It's explained in the first paragraph here: S&P/ASX 300 - Wikipedia where it says: The S&P/ASX 300, or simply, ASX 300, is a stock market index of Australian stocks listed on the Australian Securities Exchange (ASX). The index is market-capitalisation weighted, meaning each company included is in proportion to the indexes total market value, and float-adjusted, meaning the index only considers shares available to public investors.

So perhaps the free float of CU6 is as high as 70% of their market cap, or around $490m, but probably less if all of the outstanding options were exercised.

DVP's market cap is now down to around $595m, of which 15.1% is owned by Bill Beament's Precision Opportunities Fund Ltd and another 14% is owned my MinRes (MIN), so the free float could be around 71% of $595m, or $422.5m. But DVP were trading higher than they are now in recent months, so perhaps the calculation was done when DVP had a higher market cap and CU6 had a lower market cap - like at December 31st, when CU6 was $1.90/share (now $2.66/share) and DVP was $2.83/share (now $2.51).

Hope that helps.