Another thought, does GetScrollPos give you any information that you can make use of?:
DEFINE VARIABLE hPos AS INTEGER NO-UNDO.
DEFINE VARIABLE vPos AS INTEGER NO-UNDO.
RUN GetScrollPos(FRAME FRAME-NAME:HWND, 0, OUTPUT hPos).
RUN GetScrollPos(FRAME FRAME-NAME:HWND, 1, OUTPUT vPos).
MESSAGE...