Could still be temperature if the thermistors on e printers read differently--that is, the same setting doesn't necessarily work out to the same physical temperature on two printers, even if they're the same model, because the thermistors vary. My suspicion would be that you're printing a little hot, and the filament is contracting after it's extruded. On the first few layers it can't shrink much because of all the material in the middle, but on the vase mode layers there's nothing preventing it.