Static fluid boxes

I am using Captivate 2017, and I have been having some trouble with static fluid boxes. I am currently designing a training program with three fluid boxes (top-title, middle-content, bottom-button to go to next slide). Pretty simple. I placed one text caption in the middle fluid box. I made the middle fluid box a “static” fluid box, because it also contains some shapes that I would like to partially cover the text.

An issue comes up when I try to preview the project. The text and shapes are placed exactly where I want them to be in edit mode, but when I preview the slide the text inside the text caption increases in size while the shapes stay where they are. This is a problem because I need the shapes to align in the exact right position over the text.

Does anyone have any suggestions on how to fix this? I would appreciate any advice you have.

Thank you!