The canvas display on userlist grid usage is CSS driven. You'll need to adjust the CSS to have larger canvas there. The below should work. change the 150px to whatever height you want.
Code:
.cb_template .cbUserListDiv.cbUserListLayoutGrid.cbUserListCanvas .cbUserListRowCol1,
.cb_template .cbUserListDiv.cbUserListLayoutGrid.cbUserListCanvas .cbUserListRowCol1 .cbUserListFieldLine,
.cb_template .cbUserListDiv.cbUserListLayoutGrid.cbUserListCanvas .cbUserListRowCol1 .cbUserListFieldLine > .cbListFieldCont.cbUserListFC_canvas,
.cb_template .cbUserListDiv.cbUserListLayoutGrid.cbUserListCanvas .cbUserListRowCol1 .cbUserListFieldLine.cbUserListFL_canvas .cbImgCanvas {
height: 150px;
}
If you need any of the other elements re-positioned right click and inspect element on them to review their CSS.