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.