Run production has been a big problem for him. He's fourth on the team with 28 runs scored tenth with 11 RBI despite having the third most plate appearances.
Tabata has spent a lot of his time in the lead off spot. That has led to 70% of his at-bats being with nobody on base. In those at-bats, he's hitting .232/.295/.363 with ten doubles, three triples, and two home runs. For the year, Tabata is hitting .226/.288/.339, so he hasn't been better or worse with nobody on.
The issue with Jose has been getting hits with runners on base. Obviously you aren't looking for him to be a big RBI guy, but you still look for your players to drive in runs when they're on the bases. With runners in scoring position, Jose hits .194/.275/.306. With men on base he hits .211/.273/.282, just really poor numbers.
I did some messing around with Microsoft Excel this morning and came up with a pie graph that breaks down Tabata's at-bats with runners on. You'll see the frequency of every possible situation and how he hits in those situations. Here's the graph:
