If you always use text styles with InRoads symbologies, you should use a scale factor of 1 in the Global Scale Factors of InRoads.
If you assign the Line Style Scale in the Models Properties dialog box to Annotation Scale, you should use a line style scale of 1 within InRoads.
As someone coming new into these products, you are actually pushing the limits of many of us long time users. For many of us, we have clients who are behind in releases and adoption of many of these items, as they are not something that has always been possible. So, keep in mind that you might become an expert on some of these before us.
For example, our main client has not assigned any symbologies in InRoads that use Text Styles. So while non-InRoads text will honor annotation scale, the InRoads text does not. Also, in the Line Styles settings, there is the ability to assign a "Physical" property to line styles. When done, these linestyles do not react to annotation scale. Although our client has linestyles that represent real world objects and should always be used with a scale of 1, none of these have been assigned the Physical property. So if we turn on that Model Properties settings, they will scale.
One issue with using annotative text with InRoads is that the other elements and offsets that go with the text will not react to annotation scale.
So you may find that text styles in InRoads are not quite where they need to be.