Please note, Shell fitting is not an exact science, and depends on personal preference too...
If you've looked at the above charts and you still can't decide, then use these guiding principles to get you through these tough times:
1. Keep in mind, for most camera/lens sizes there are 2 Shell sizes that will fit your camera. So, this isn't a life or death situation.
2. Shell is made to stretch and fit your camera snugly. For any given camera size, a smaller Shell will fit your camera more snugly and a larger Shell will have a baggier fit.
3. A tighter fit is better for carrying your camera in Capture since everything will be nice and snug. A looser fit is better if you plan to actively shoot with Shell in the rain since it will be quicker to pull Shell up and access your controls.
4. Even if you get the larger Shell size, it will be much more snug-fitting than other camera rain covers on the market. Another advantage of picking the larger size is that you can cinch Shell closed all the way around your camera, even when using long lenses with hoods.
5. If you have a DSLR and a mirrorless camera, consider getting 2 Shells. You really don't want to use anything bigger than the small Shell for a mirrorless camera.