I am trying to create an alternate layout of a book by narrowing down the width a bit. But every time I try, the margins on the master pages also narrow down a lot because their edges stay relative to the page edge. I need them to stay as they are - to keep the width of the inside area fixed. I have tried many different options both using autoadjust and not, and trying different Liquid Page Rules - all with same result - the margins scale with the page...I am thinking that I might be missing something obvious, but what?
It looks to me like your image area is what's scaling—the space between the left and right margins, where the content goes—but the margins appear be constant. Check the left and right margin values before and after to confirm. I think you want the margins to scale so that the image area will remain constant?
How about changing the paper size, as per your second screen shot, and then use File > Adjust layout to reduce the l/r margins to regain enough space for the image area?
Yes - that's what happens - the margins always stay constant no matter which option I choose during conversion.
So what I did in the end was exactly as you advised, but to achieve the result I need, I had to do the readjustments several times manually: After changing page size, first I had to fit all the margins on master pages to the tex boxes that lost their place by turnig autoadjustment Off. Then with autoadjustment On, I readjusted the all the margins again to my desired dimensions, and all the text boxes readjusted along them. I still had to fiddle a little bit manually after that.
But I wish there was a way to achieve that without going through all this hassle...