This is just how I do things - might not work well for you.
Everything I edit in a form is either inside of a section or inside of a layout table.
I work on 630 pixels wide as a pretty good fit for A4.
When I create section controls I immediately go to it's properties and set the margins and padding to 0 and turn off the borders.
This is equivalent to making the section control 'borderless' when they format on the page.
When I use the Insert Layout table function and the form page setup is set to portrait I find it defaults to 629 pixels.
It gets more difficult to be sure of the layout width when you start having section control within section controls as the design view shows the outlines of the controls and this makes them all look wider than they actually are.
However, if you stick to putting 630/629 as your total width on sections and and table column sizes it becomes routine.