It most certainly matters but again is going to be such a finite element in the tuning I wouldn’t go nuts with it. Factor in the length of the system between the merge and the beginning of the silencer and you’ll be right on par with where you need to be. Factoring in the silencer is going to require some fluid dynamics and factoring in the rapid expansion of the pulse within the volume of the silencer body.
I’ll post more on the tuned pipe theory later, and link you some ceramic packing as well.