Simultaneous TNT blasts produce different sculk frequencies

The desired result was to create a door that could only be opened when 2 players had TNT explode at the same time.

When I ignite 1 TNT at a time, the corresponding sculk sensor correctly identifies the sound as a frequency 15 explosion.  However, when using redstone to activate both TNT at the same time, the left gives a frequency of 15 while the right side gives a frequency of 8 (most likely "hit Entity" flag).  This is done in a single chunk as well.

Not sure if this is an intended mechanic of TNT or an issue with the sculk.

img 1:  the setup before the ignition

img 2: after TNT explosion, only left side has the frequency of 15.  Note both sculk have received signals from their respective explosions.