This is not possible using the title attribute, but you can achieve this effect by creating your own tooltip. You can create the tooltip by scratch if you want, but Lighthouse Studio has a built-in ToolTip function that may be helpful for you.
You can create the image and tooltip with this:
[% ToolTip("<img src='" & GraphicsPath() & "info_icon.png'/>", "My tooltip text") %]
And then change the font size by adding this anywhere on the page: