Executing a Compare strategy in which a SQL Source input DDL file is compared to the Target SSID and the Target tablespace does not specify a DSSIZE; it is not changing the DSSIZE on the Target object.
In the RULESET for the Compare strategy, the Tablespace TYPE dictates whether the Tablespace can convert from a TYPE of blank (no DSSIZE) to LARGE. By changing the Tablespace TYPE rule to "Y", the DSSIZE is able to be applied to the Target tablespace as desired. A "Y" settings tells the Compare that this attribute should be compared for any changes otherwise it is not and so the existing target value is unchanged.
Compare Rule Database Services