To help with your navigation setup, try using the new visual aid feature on the tabbing palatte in Designer 8.2. It is a very useful tool in helping figure out custom tabbing navigation.
You can set it on by clicking the top right dropdown on the tabbing palatte, and scrolling down on the context menu to Visual Aids. Click it to set it on.
When you then mouse over fields on the canvas, the containers will highlight orange, and an arrow indicator will indicate the next object in the order.
If you set an object to be tab-able, but it is unavailable at runtime, because it is protected, or is hidden from the layout for example, the default tab order will kick in, and go back to geographic order, which may not be want you desire.