Positioning of compositions on Ipad

Hi All,

I'm having an issue with trying to position some compositions on the ipad version of my site.

I have four compositions on the page. Each target box sits in exactly the same place like this....

However the problem is when I view them online, they sit in different positions (either too high or too low). Also each grey box seems to be slightly smaller. There is no scrolling applied, so I can not work out why I can't make them all sit in the correct place and correct size (i.e. exactly how they appear in design view)