The grid doesn't currently support this - you are going to have to 'shrink' the grid yourself. You can easily set small fonts and row heights as follows:
_shinobiDataGrid.defaultRowHeight = @15;
_shinobiDataGrid.defaultHeaderRowHeight = @15;
_shinobiDataGrid.defaultCellStyleForRows.font = [UIFont systemFontOfSize:10.0f];
_shinobiDataGrid.defaultCellStyleForHeaderRow.font = [UIFont systemFontOfSize:10.0f];
But it's up to you to work out the fonts and heights you need!