ASX 300 Club, page-10

That's a somewhat misleading representation because it looks like what you've presented is based on MC only.

On an MC-only basis, the entry price to the Top 300 (not the S&P/ASX 300 index) would be close to $900m today (https://www.marketindex.com.au/asx300 - re-sort the MktCap column to Ascending Order, in order to see the lowest MC in that Top 300 list).

However, that's not how the S&P/ASX 300 Index is calculated. It's based on a liquidity- and float-adjusted market cap methodology. Depending on circumstances at the time of the Sept 2021 rebalancing Reference Date (done in August), a new entrant to that list could very well have a significantly lower MC than ~$900m. S&P Gobal's product data page for this index shows a Minimum Market Cap for its constituents as $226.96m (link). Presumably this is not a live number, but was the minimum on the Reference Date of the last quarterly rebalancing (i.e. in May, 2021). That hurdle is likely to have risen since then, due to the current bull market.

By way of example, the vast majority of the current batch of additions were north of $1b MC, (crudely) based on today's closing SPs, not the mid-August Reference Date. There was one notable exception, however, being Strike Energy (STX) which closed today with a $526m MC. It's MC around the time of the August Reference Date was closer to $660m.

If we (very, very, crudely) strip out the combined 25% cornerstone holdings from our total SOI (as being not available for free float), then we're left with ~2,300m free-float SOI. At today's closing SP that gives a float-adjusted MC of ~$275m and not too different from the ~$250m float-adjusted MC as at the Reference Date in August -- well short of STX's metrics.

This very simplistic and somewhat bastardised approach doesn't properly consider the true MC methodology or relative liquidity hurdles, or a bunch of other relevant criteria (link), but it should hopefully give a very rough idea of where POS currently sits.

All going well the Dec rebalancing might be the quarter...