I’ll take a stab at this one…
First, what is the purpose of increasing the main bar section width? Do you need to fit some equipment in that space?
My guess is that nobody has ever tried increasing the width so, at first glance, it looks like 23.5 should be 28.5.
99.9% of builders use this tool to lengthen or shorten a section. Can’t say I’ve ever tried modifying the width, but maybe the original designer can weigh in on this.
My guess is that the width of that section is not really advised, especially since it has a 30″ limit. Any modification beyond that and you would just use the red highlighted changed parts and extend at will.
I use this tool for custom bars projects I build for clients, but always use it as a guide, not the final word.
In a lot of cases, I see the sheeting does not change, but if that is the case, you just measure against the frame you have modified.
Again, I use it as a guide.
Hope that helps a bit.