What version? in v1.38 check the documentation here:
v1.38 documentationand search for "zoom": plenty (!) of parameters related with zoom and gallery can be used to adjust the behavior, as you like it.
E.g.
Name Type Defaulticonpos {bottom, left, right, top} or two positive numbers bottom right
In v2.0 everything related to "gallery" was consequently renamed from "...zoom..." to somtehing like "...gallery...", since with v2.0 we introduced a "real" zoom.
You will find information about all this in the
wiki (here link to migration hints)