Hi Mark,
Yes that's sensible.
I was trying to understand whether there would be any circumstances where having neither fix separation=on or contact region is desirable.
If there was no contact region then wouldn't it be better that it be impossible to switch off fix separation? It may take a moment or two for the user's penny to drop as they (me) try deselecting 'fix separation' for the unpteenth time ... followed by a conscious effort at creating a contact region.
Otherwise we could have odd fastener behaviour disguised by the results of a more complex model.
Thanks
Charles