Turns out my brain just doesn't work properly and the difficulty multiplier was turbo-broken the whole time.
I'm rolling out an update ASAP to fix this, alongside a couple of tweaks.
Thank you very much for the input! I appreciate the idea of people wanting to share and compare their scores with the difficulty multipliers, I'd definitely love to see if I can do anything in the future to make it a bit more convenient.
I initially worried about the difficulty of the game, but I think I accidentally made it way too easy in doing so. I'm hoping to get new pirate variety, etc... To give the game more flavour and difficulty.