Well here is my best explanation.
In your base drawing (where your work is) the Ltscale should be half the Dimscale. So that means, if the floor plan, or in your case the site/ civil plan is 1"=30'-0", the Dimscale would be 360 and the Ltscale should be half, or 180.
Now when you xref that drawing in the plot drawing, or another drawing that has the titleblock in it, that Dimscale in model space is still 360, but the ltscale is now 1! If you make the mistake like i have so often seen, and make that Ltscale 180, all the linetypes in the Xref are now at 180x180 and you will see all solid lines where their should be definitive linetypes throughout the drawing (or the Xref). In the drawing that you xreferenced any line drawn will be fine, if the Ltscale was 180. But again this is a No-no.
So basically, the whole idea is you have the base drawing that has all the work in it where the Dimscale is set to the proper scale,(ie. 1/8"-1'-0" would be 96 or 1"=50'-0" would be 600)and the Ltscale is half. When you reference that base drawing in the plot drawing, anything enetered in modelspace of the plot drawing would still need a scale of 96 or 600, but the Ltscale is 1. You dont want the Ltscale to get multiplied.
The big problem arises when you scale any specific line to anything other than 1.00. My suggestion is leave it at 1 and see what it looks like in the plot drawing, not the base drawing where the line actually resides. From there slight ly bump up/down the value for that specific linetypes scale.
I knew it probably wasnt the PsLTscale but its ggod to get familar with since it can play a lrge role in linetypes not comong out properly. Something to be aware of.