That's because most of the interface spacing and space allocation is handled in faction.ini.
Most of these sorts of things are handled by X and Y offsets, and a matching constraint X and Y pair.
I have married and updated RAS Clear & Pure v13 (with v14) and when I was creating a new expanded chatbar, simply modifying extmssgbig.png does not satisfy these requirements. In order to obtain the proper X and Y positions on the screen to match with any modifications, I had to go into faction.ini and modify, for example, "IntAddMessWindow" to set the proper X and Y for the image, and then to place the chat inside it within proper dimensions, I used "IntMessLarge".
Of course, if this element is governed by a resolution case structure, ensure that these resolution changes are being applied underneath the proper section (i.e., 1920x1080 changes section). However, since I suspect that this is a global section (barter), I'd say just search for "BarterMain", "BarterCont", and "BarterOffer". In my section, this image is governed by "barter.png". Try poking around in there.