I think those 100k, 200k orders on the buy side aren't genuine.
My reasoning:
74% of the shares on issue are held by just 4 holders (per page 45 of the annual report). Of the remaining 26%, I think it's safe to assume it's mostly distributed among smaller retail holders.
So there are very few holders with very large parcels of shares to sell, and if they aren't selling their shares, your big orders just aren't going to get hit.
The only way your orders will get filled is if small holders sell all at once, in a panic sell stampede of sorts. But if you've got your ears to the ground you can always pull your orders as soon as there's an inkling of this happening.
In other words, you can safely place very large buy orders on the buy side without fear of them getting hit.
And if you know this, would a rational SPT shareholder not use this fact to achieve a better price for shares they wish to sell by stacking the buy side beforehand?
Anyway, just my theory. It's fascinating to watch how this stock day trades.
Edit: and... the large buys disappeared while I was writing the post, lol. Of course that happened.