not to undersell RX, but MACE offers a 6mm (1/4"), 12mm (1/2"), and 25mm (1"). so as far as im aware, its not a fitment issue as to why one vendor is preferred over the other. so far, the only issues have been with the varaam CAI. i haven't even seen reviews posted on RX's products unless i missed something. but to answer your question, yes, size does matter
you want the longer runner length for a better gain in TQ.