Could you use the custom data rules feature on the table instead of a form rule? I believe that works in grid edit reports as well, it won't allow records to be saved if they do not match your data rules. You could make sure that the field is only under a certain number with that but number validation can be tricky. In this case at least it should only be 2 digits and does not have any separators.
I think the simplest version would be something like this.
if(
[Remaining Inches] > 11,
"Remaining inches cannot be more than 11"
)
That should stop anything from being saved that is more than 11 in that box but it may not solve for decimals if they enter those. That could possibly be done at the field level settings though.
