DMDX Help.

Y Position Keyword

<YPosition N>
<y N>

    Deprecated Y switch alternative, use <xy> instead (there are logical conundrums when only one axis is positioned and <xy> obviates them). When using the DMDX form (a keyword delimited by <> as opposed to the original DMTG form) N can either be an integer or a real number. If N is an integer it is a pixel value, if N is real it should be between 0.0 and 1.0 as it is multiplied by the height of the screen.
    By default Y determines the coordinate of the top of the displayed item, see

DMDX Index.