Yup, it seems to me that the optimal missile would use mid-course guidance before doing IR / visual light homing in the terminal phase.
The techniques they used to decrease the IR visibility are pretty neat. The engine nozzles are over the wings and there are a lot of airflow tricks used to cool it down faster so from below there might not be enough plume to track from a surface launched missile coming, from below at least.
https://en.wikipedia.org/wiki/Northrop_Grumman_B-2_Spirit#In...
When you’re talking about terminal IR guidance on any modern missile, generally the IRCCM will be so good that the probability of defeat with a flare cocktail is below an acceptable risk threshold. DIRCM is the current answer to this problem and—to tie this in with the parent comment—renders terminal IR guidance much less effective than MMW or other RF guidance.
https://en.m.wikipedia.org/wiki/Directional_Infrared_Counter...
It's impossible to hide from long wave IR sensors, which detect the heat signature of the plane itself, and not its exhaust.