The initial value of the StopAfter property of the SmartBusinessEntityAdapter is defined in the products.i file:
    /**
     * Purpose: Value for StopAfter to be passed to the Service Interface
     * Notes:   Allows limiting the execution time of queries executed on the backend
     *          Not supported on OpenEdge 10.2B
     *          The default value for this property may be set using the DefaultStopAfter
     *          preprocessor variable in Consultingwerk/products.i
     */
    DEFINE PUBLIC PROPERTY StopAfter AS INTEGER INITIAL &IF DEFINED (DefaultStopAfter) NE 0 &THEN {&DefaultStopAfter} &ELSE 0 &ENDIF NO-UNDO
    GET.
    SET.
Alternatively it's using the DefaultStopAfter value from the .applicationsettings. But this is just a property default - it won't override a setting defined in a Form.
To enforce the same value to all instances, I would recommend to override the OnNewFetchDataRequest method of the SmartBusinessEntityAdapter and set the value there.