I understand your confusion because I myself, and I'm sure most reloaders have had the same problem. What I do know about H110 is that it works best when there is very little or no airspace in the case. I know that's not always possible but the closer you get to it the better the load shoots.
As an example, the max charge recommended by Hodgdon for a 158gr Jacketed bullet in a .357 Magnum is 16.7gr. When I filled the case to just under where the bullet would touch the powder and weighed it the charge was 16.8gr. I don't want to load a round that heavy for my handgun and tested a few lighter loads and came up with 16.4gr as shooting best in my revolver. It's not quite filling the case but it's close. I also found the accuracy, ES and SD goes down fast when I lighten the charge much below 15.8gr so the fuller the case the better.
The above is just my experiance with my revolvers but I'm sure those who use H110/W296 on a regular basis probably found what I said to have some merit.