This graph:
https://www.aulro.com/afvb/images/im...016/02/403.jpg
and this statement:
The radiation energy per unit time from a blackbody is proportional to the fourth power of the absolute temperature (My emphasis)
should help explain why a shield helps more than you might think.
Radiation Heat Transfer
Even though the calculation for the amount of radiated heat refers to absolute temperature, a small drop in temperature makes a big difference to the radiated heat.
The shield only needs to be a few degrees cooler than the body of the turbo to make a worthwhile difference.