I usually use the "French Plunge" method (recommended by Carol (readinglady), Melly and Annie among others) and that has solved my personal floating fruit problem.

Here's part of my post from an old Strawberry Rhubarb jam thread describing what I did:

"I did use the French plunge method - took the fruit out, cooked the syrup a little yesterday, put the fruit back in to steep in the sugar syrup and let it set overnight.

This morning, I strained the fruit back out and cooked the syrup to 220 degrees, put the fruit back in, returned to a boil and BWB'd."

Allowing the fruit to absorb the syrup and equalize overnight, it tends not to float. I do the same technique with marmalade.

I still do twirl the jars before they set firmly (still warm but not hot - I sit them on the counter and spin 'em around in a circle. I don't turn them upside down if I can help it). That helps distribute the fruit a bit more evenly, too.

Hope that helps.