I wouldn't say the Small feels smaller - it feels like everything is closer together within the bag instead of so much space in between items in a Medium. The Small is somewhat similar to what the Small long-handled nylon holds.
I have more Smalls than Mediums because I find that the Small fits my day-to-day needs. I started off with 2 Medium Cuirs before buying my first Small because the Cuir is so smooshy that even when it's a Medium, it doesn't look too big and yet it offers the flexibility of more space. Now with my 2 Mediums, 4 Smalls, 1 Large long-handled Cuir and 1 Mini Cuir, I feel like I have enough flexibility with space that these Cuirs offer