Why is it that no matter what you set the default sill height to when creating a window it will ALWAYS come in at something else...
I have also tried to create a head height parameter to get my windows to come in at the correct height and they still come in at something different. This is starting to get very frusterating...
Since there is no way to establish those defaults in the project, it would require to do some minor changes to the families: the sidelight family, and the other windows.
Although it would be better if revit had a "head height" setting the reality is that it has a "sill height".
In your window family you can preset parameters of height and sill height to always add up to the intended head height : (e.g. assume 2000 for head height) e.g.
1500 h window has sill height of 500
1000 h windows has sill height of 1000
400 h window has default sill height of 1600
These can all be preset in the family types, and they will all insert into the project with head height at 2000. This is the work around that I use. Hope that helps.