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The most common cause of star bloat is out of focus IR light. This typically occurs with refractors and other lens designs as wavelengths reach focus at different points. Mirror based telescopes focus all wavelengths equally, thus don’t exhibit this characteristic. Another thing to consider is that not all IR blocking filters and coatings are created equal. There are differences between manufacturers – some start at 750nm others may be lower or higher. All filters can leak IR, but more so the red filter considering its transmission wavelengths are very close to the start of IR. In some cases, poor quality filters will actually have an overlapping transmission window where major IR leaks can occur. IR contamination with CCDs should be avoided at all costs – especially when colour imaging.
You could try using a UVBRI filter set mapped as R=R; G=V; B=B. I’ve seen some incredible images taken with this combination. There is typically some cross over between R and I, but with the right coatings this is minimised. I've also assumed that your filters are parfocal, so no need to refocus between filter changes.
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