There isn't much undercut on the sidepods. In recent years it seem to be de-rigueur to have the base of the sidepod under the radiator inlet to be narrower than the inlet, and then continue to be narrower at the floor than the cooling tunnel that vents around the upper wishbone.
The RB13 does are this trait. Is the whole package so tightly wrapped that they have basically done away with most of the cooling tunnel and just have the small exit vents at the wishbones?
There is no undercut at all at the 'dB' of RedBull