ice packs in cool bag - on top or underneath?

[Valynand]

Is it best to put ice packs on top of or underneath the food in a cool bag?
Cool air is denser and sinks, which would suggest that the ice pack should go on top, but I'm guessing more heat is actually lost through conduction than convection. The cool bag https://under-the-open-sky.com/best-backpack-coolers/ will be sitting on a car seat so there will be foam rubber (or whatever they use as filling in car seats) underneath it, but it will be exposed to the air on top. I suppose the seat will provide further insulation so most of the heat will be lost to the air through the top of the bag, which I guess also suggests that on top would be the best place to put the ice pack?