I don’t fully understand your question 1. All boundaries must have a defined type. In mfix/model/init_namelist.f you will find
BC_TYPE(LC) = UNDEFINED_C
I suppose you could try changing this to BC_TYPE(LC) = 'NSW' and see what happens.
Regarding question 2; the answer to this is displayed in the ‘tooltip’ which appears when you hover the mouse over the relevant control.
Perhaps we should add this text to the user documentation.
– Chares