With ExtJS used in examples:
Code:
var store = Ext.create('Ext.data.JsonStore', {
    fields: ['name', 'data1', 'data2', 'data3', 'data4', 'data5'],
    data: [
        { 'name': 'metric one',   'data2': 12},
        { 'name': 'metric two',   'data2': 8},
        { 'name': 'metric three', 'data2': 2},
        { 'name': 'metric four',  ''data2': 14},
        { 'name': 'metric five',  ''data2': 38}
    ]
});

Ext.create('Ext.chart.Chart', {
    renderTo: Ext.getBody(),
    width: 500,
    height: 300,
    store: store,
    axes: [{
        type: 'Numeric',
        position: 'left',
        fields: ['data2'],
        title: 'Sample Values',
        grid: true,
        minimum: 0
    }, {
        type: 'Category',
        position: 'bottom',
        fields: ['name'],
        title: 'Sample Metrics'
    }],
    series: [{
        tips: {
            trackMouse: true,
            width: '100%'
        },
        type: 'scatter',
        markerConfig: {
            radius: 30
        },
        axis: 'left',
        xField: 'name',
        yField: 'data2'
    }]
});
As for me, Expected result is about showing tips when cursor is anywhere but above whole bubble.
But Actual result looks like hint is shown only if cursor is over the center ±10 px. I investigated that this is because of Ext.chart.series.Scatter.isItemInPoint code. It does not count bubble's radius while checking "point is inside of marker".