I can think of two ways to do this, however I am not at my computer to check it out, so my instructions may not be accurate.
1. For all images in your tour. Before you add any images to your project, set the FOV preferences to your desired value. To do this, go to Edit > Preferences > Scene, then in the FOV boxs, set Initial: 87, Min: 87 and Max: 87 or to your preferred value. You will have to remember to alter that back for your next project.
2. For selected imags in your tour In the main window, and with the image selected, go to the Properties and Actions at the bottom of your screen and alter the three FOV values, naking sure all are the same value.
I hope this answeres your question.