I see, thank you.
Let's take for example the missile launch effect. It may engage 3 samples:
hp_11_0_L.wav - left
hp_11_0_M.wav - middle (both)
hp_11_0_R.wav - right
The samples contain 3 sets of waveforms as on the screenshot attached.
hp_11_0_L.wav sample activates only bass-shaker connected to the left channel,
hp_11_0_R.wav sample activates only bass-shaker connected to the right channel,
hp_11_0_M.wav sample activates both bass-shakers.
In your case it's going to be felt unnatural. So, you will want to modify the samples, which is not hard. Basic information you can get in the User Guide https://simshaker.com/guides/sound
Important: at this point we have to clearly understand how do you want it to be felt.
If you want it to to be felt in the butt area only, you should keep the waveforms only in the channel connected to that bass-shaker. Let's say it's connected to the left channel. In such a case make all 3 samples as hp_11_0_L.wav.
If you want it to be felt in the backrest area only, make all 3 samples as hp_11_0_R.wav. Assuming that the backrest area bass-shaker is connected to the right channel.
If you want it to be felt in the both areas, make all 3 samples as hp_11_0_M.wav
For simplicity sake, you can make 2 copies of the reference sample and give them the others names.
Is this clear to this point?