Distance between post and floating bar changes

Hi,

the distance between floating bar and the post on my blog http://www.upgradeyourmind.it” class=”bbcode_url”>http://www.upgradeyourmind.it is not always the same. It changes: sometime it’s near the post:

http://www.upgradeyourmind.it/successo-2/jim-carrey-sogno-divenuto-realta/” class=”bbcode_url”>http://www.upgradeyourmind.it/successo-2/jim-carrey-sogno-divenuto-realta/

sometime is on the edge of the screen:

http://www.upgradeyourmind.it/autostima/resilienza/” class=”bbcode_url”>http://www.upgradeyourmind.it/autostima/resilienza/

How can I fix it?

Thank you

Matteo