Of course it can matter where the orders are routed. PACX used to be the worst for these odd-lot fills, while CBOE never did. At the time, there were better incentives for some brokers to route to PACX as I recall. Also, it seemed to be when I improved the market to the NBBO on PACX, since there was no MM in that particular class willing to make a tight market (on either side).
Listen to the experienced traders - if you think someone is trading specifically against you, and you're not yet doing/quoting 10% of the volume in an instrument, you're being paranoid.