Setting separate drawing scales for two files open at the same time

I am drawing house plans for a remodel. To get them precise I’m preparing drawing elements at 1:1 scale - which I set in the Dimension settings tool. I want a separate file at a scale of 1:48 for printing at 24”x36” open at the same time to paste various drawing element into for final preparation and formatting. AI responses online say that when I open the Dimension settings in one document those settings are for that document only and that I can set the other one at a different scale. I’ve done that several times and it does not work. Either I’m missing some setting to limit the choice to a single file or those instructions are simply wrong.

Anyone have any experience with this and suggestions?

Thanks!