I would fully support giving all force fields a minimum size (maybe a percentage of their full HP size). If nothing else, this would be great for armored force fields, and also Spirecraft Shield Bearers too.
There is also a suggestion on mantis to make the HP to forcefield radius a non-linear relationship for armored forcefields, where it would shrink less per HP lost compared to normal forcefields for high HP remaining, but shrink faster per HP lost compared to normal forcefields for low HP remaining, so they can still shrink down to maintain survivability.