Compound systems / wastegate

Hello,
I came across this video of Thailand drag trucks.

They use compound turbo systems.

However, it seems that they dont reintroduce the HP wastegate's outlet before LP stage. (wastegate on collector, before small HP turbo dumps to open air)

Is there a strategic reason behind this ? To me this is wasted energy not going to spool the LP turbo.
But maybe the HP turbo runs more efficiently because of the greater pressure delta /expansion ratio ?

At 1:40 minute mark
Diesel Race Truck on the Streets of Thailand *120 PSI* - YouTube

My guess is adding exhaust pressure between the turbos can slow down the manifold turbo and become an airflow restriction.