k1vsk - I respectfully disagree with your logic. You don't pull half the amps from each battery. More current flows from the larger battery than the small one. This is regulated by the voltage from each. If the voltage starts to drop in one battery (because it is smaller) it will just supply less current until the voltages are equal again. When charging, if one battery received more current, the voltage would rise in that battery and current going into it would decrease. It's a completely self regulating system.
This is a very important point -> It is true that you should not mix and old battery with a new one, but this is more like mixing types (AGM, wet, or gel) than anything to do with size. As a battery ages the chemistry changes.
There is no difference in a system with one large and one small battery than a system with many batteries. For example with a 6 battery setup, from the prospective of any single battery there is no way to tell that it is connected to 5 others or one that's 5 times larger than it. The entire system acts as one large battery.