Based on the link you sent (joets.be/test/index.html), the reason this is happening is because you have an anchor tag inside the heading elements.
The <a> inside the H2 has font sizing styles attached to it, whereas the one inside the H6 does not. If you apply your 1.2em styling to the <a> instead of the headings, then that will work.
So essentially, do this:
h2 a, h6 a{ font-size:1.2em; line-height:1.2em; } Edit: I've looked at the CSS file itself, can you just remove the "h2 a" from line 339?