I think both methods of placing a baggie on a colony have their good points. It depends totally on what YOU want to do. With the baggie placed directly on the top bars, yes the sugar syrup would remain more warm. But....I always have warmish syrup that I give to the bees (inside house temperature). I don't feed cold syrup, ever. I am pretty sure that the warmth from the colony would keep the syrup in the baggie pretty warm when it is on top of the inner cover. The speed in which the bees consume a baggie of syrup, I prefer to put it/them on top of the inner cover. That inner cover can hold a lot of syrup in baggies. That way I don't disturb the bees by lifting up their house roof and I can feed them a baggie any time I want, rain, snow, whatever the weather conditions.
Natalie, dry sugar is more work for the bees, they need extra water for the dry sugar, sugar syrup they just suck up. Beautiful day in this great life. Cindi