Most physics interfaces add a default pair feature that includes all pairs under the Definitions branch, for example, the default Continuity pair in Figure 5-6. It is not possible to remove any of the pairs selected in the default pair feature. If you do not want to use one of the pairs under Definitions in your physics interface you can select the Disconnect pair checkbox to disconnect all the pairs. The default pair feature will then not contribute with any conditions, and the fallback conditions from the other boundary condition will apply on the entire selection of the default pair feature. Then add a new pair conditions to your interface where you are free to select the pairs to use.