Looking at the source code of an IWP page illustrates this.
I would try a Layout specifically for IWP that has green periods . . . . . to force the layout design.
Posted, Rethought - period padding will not work.
You have much greater control with Custom Web Publishing, with greater complexity.
Google "IWP design display filemaker"
IWP Limitations and design workarounds
Top 10 Instant Web Publishing No-No’s
You might make 5 copies of your field for this layout. Format each copy of the field with a different single value value list.The first copy would have a value list of just 4, the next to the right would use a single value of 3, and so forth down to 0.
Now you can align each single radio button copy of the field with the corresponding label text above it.
I like the idea of 5 copies of one field. This corrects the spacing issue in IWP, but each field now acts independently in IWP (but not in the native program) allowing for multiple radiobuttons to be activated.
Bummer, I was sure that I'd seen that work elsewhere, but now I am remembering that the other case used check boxes where multiple selections were not an issue.
I think I'd replace the check box field on this layout with buttons that enter the data into the radio button field.