Line based families are a great way of producing flexible
Revit components, but there is a feature that may not give you the results you
are after.
When you have 2 line based families next to one another they
like to automatically join with one another, this is just at feature that
occurs in this type of family. The only problem is that there is no disallow
join feature (like the wall tool).
The magic number is 32mm, any closer and the components will
automatically join.
If you need to have components closer than 32mm you may have
to switch to a family with instance parameters, then you can get a close as you
want without the components automatically joining.