It is most definitely because they were invested before the...

It is most definitely because they were invested before the company was listed.
Since they took a major risk (and all) by investing when the company was private, meaning they would have also spent a considerable sum at that time to get the mineral sands JORC MRE up.

Not to mention that the

We won't know the exact price they paid, but it seems when they listed they took a $1.5 million cut to their total investments - everyone invested at the start. the total losses were at $3.65 million, ie. roughly how much they may have put in total. In latest report it states $1.6 million after consolidation, the acquisition cost of Mozmin by HVY was adjusted, see below at page 49.

see page 46 and 49
https://hotcopper.com.au/threads/ann-prospectus.6279293/

Now would you be willing to take this risk and put in your funds in an unlisted company for a number of years not knowing if you will lose it or get listed? I don't think so. It seems they actually lowered their valuatin and took a cut, public shareholders actually benefited from this, not something you see often. However looks like they should have listed at a higher market cap, which they could have easily gotten since the offer period was closed extremely fast from what I remember within a day or two, markets are just too short sighted.

Why you see the entry of some looks like it is way below at 5c or so is because they already had shares (when private) and when they put in a notice of substantial holdings, they are merely stating the amount they paid for the current on market purchases not the total.

As an example -
1) They already have 2 million shares, which they paid say $1,000,000 for before listing
2) Now they buy another 1,000,000 shares @ 20c, which is $200,000
3) They would state in their notice 3,000,000 shares and total consideration paid is $200,000
4) This would make it seem as if they got their shares at 6.7c, which is not right, but that is how the ASX notices are to be filed.