Your sample size is basically meaningless but have a look here:
http://www.runitonce.com/chatter/joe-ingrams-take-on-zoom-vs-regular-cas/

You'll probably need at least 100k hands before being able to compare the two. At that point if there's still a stark discrepancy, I'd say it's because 1) The games are tougher in Zoom as you said, or 2) The lack of reads in Zoom is causing you to play poorly.

Hope this helps.

Even at 100k sample your bb/100 win rate can vary by at least 2bb/100! I won't post link but try googling 6 max variance calculator and runnning some sims