Kinda late answer.
I've solved the same issue by redefining c3 core functions getXAxisClipX and getXAxisClipWidth to the following
c3.chart.internal.fn.getXAxisClipX = function() {
var $$ = this;
return $$.getAxisClipX(!$$.config.axis_rotated) + Math.max(30, $$.margin.left);
};
c3.chart.internal.fn.getXAxisClipWidth = function() {
var $$ = this;
var chartMargin = $$.margin;
return $$.getAxisClipWidth(!$$.config.axis_rotated) -
Math.max(30, chartMargin.left) -
Math.max(30, chartMargin.right);
};
Here is the example https://jsfiddle.net/vhpzma97/