Optiopn ruler right margin slider cannot be set

In the Options menu I try to set the right margin slider to 18cm. I want this as a default for all my text. However, I cannot set it beyond 16. Why?.

Firstly, this isn’t actually a margin setting, so you probably don’t want to be setting it at all (I speak for the majority of cases when I say that). This is a right indent setting, which is meant to be used to offset the right-hand side of the text inward from the margin (block quotes are a common case). Margins are set in the compiler, in the Page Settings pane.

Secondly, that’s not actually 16cm because the compiler inserts margins after you write. The ruler starts at 0cm in the editor, but that point on the page is probably going to be more like 2.5cm, so at the least when you drag the thing to 16cm on the right, that’s going to be more like 18.5cm. It doesn’t always work out to be precisely that (I’ve found right indenting between word processors can be sketchy at best). But that should really illustrate that there is no need to universally set an indent. That is what margins are for.