The issue is that when I tested out various more dense solutions (DataMatrix, colour QR codes, or HCCB) I discovered that they are difficult to scan with most m

The issue is that when I tested out various more dense solutions (DataMatrix, colour QR codes, or HCCB) I discovered that they are difficult to scan with most mobile scanners, meaning that while you can theoretically get fairly high data density on paper (no pun intended), you will struggle to actually reconstruct the original data. But if you've figured out how to get even more density without making it difficult to practically read the data from the document I'd be very happy to hear about it and would gladly switch to that instead.