That could work, but I'd argue it'd be quite excessive as you'd get 3¤4 categories for every level. The extra variable is preferable imo.

Howdy! I've started up an entry for Spiral Knights. The game supports three levels of difficulty and groups of up to four players. It's quite common to run in various group sizes, so I'd like to separate runs based on group size. While the player count placed on individual level categories would be very nice to use, I'm unable to find any feature allowing me to filter or keep groups of various size separate.

Unless I'm missing something, I think this would make a great feature. Either way I realise that features may take time to implement, if thye're implemented at all so I'd like to ask what solution you others suggest. I'm thinking the simplest way would be to add an extra variable, but would that be ideal or are there better workarounds?