Wierd isn't it ... I find that with poly hives and loads of insulation in a super on top and our really mild climate down here on the Costa del Fareham I see exactly the opposite. My local mongrels usually come through without the need for fondant and stores left in there at the first inspection .. Paynes 14 x 12 Polys with an empty super on with at least 50mm Kingspan in it.
Always loads of bees over the top bars when I look in throught the clear crownboards - very rarely clustered.
Not saying that you are wrong ... just different to me down here.