It does not support changing tooltip position by any methods.  In case of HTML tooltips, they appear not in desired position.  Next method works, it is based on my findings and own experience.

Before, it is way too left.

After, it is centered right above the point.

Use next "fixToolTipPosition" method to fix it.

var chart = new google.visualization.LineChart();
google.visualization.events.addOneTimeListener(chart, 'ready', fixToolTipPosition);
chart.draw( cdata, options);


function fixToolTipPosition() {
    var container = $('.chartDiv.active > div:last-child > div:last-child')[0];

    function setPosition(e) {
        var tooltip = $('.google-visualization-tooltip');
        var left = mouse.x - tooltip.width()/2;
        var top = mouse.y - tooltip.height() - 15;
        tooltip.css('left', left + 'px');
        tooltip.css('top', top + 'px');
    }

    if (typeof MutationObserver === 'function') {
        var observer = new MutationObserver(function (m) {
            setPosition(m);
        });
        observer.observe(container, {
            childList: true
        });
    } else if (document.addEventListener) {
        container.addEventListener('DOMNodeInserted', setPosition);
    } else {
        container.attachEvent('onDOMNodeInserted', setPosition);
    }
}