It seems not possible for current settings. However, there are two options:

1. We do setup a property called indicatorTitle with which you can set a text to show when the mouse is over the indicator. May be by hovering the indicator and you can show the text like "Compared to last month" is enough.
2. If you really want to make exactly your requirement. It is possible too but requires a little tweak on the component. You can access the koolreport/core/src/widgets/koolphp/Card.tpl.php. There, instead of showing the indicatorTitle inside html property "title", you move it outside to let it show on the card.