Paddy, according to all the web pages with techniques on this the little toe should be just fully though strap when the foots in it.
Have followed that advise and you can feel the difference in control.
Learnt real fast when I first got in straps end of last season, I had them too loose, pranged and couldn't get rear foot out fast enough. Ended up in water, but foot still up in strap on a large volume board, this isn't nice.
Here is one on setting foot straps.
http://www.boards.co.uk/articles/index.asp?article_type=25
Another is this one.
www.guycribb.com/windsurfing_technique_holiday_DVD_0076v01.htm

Mineral

hi paddy,

when driving through the balls of your feet you should be straightening your toes.

this tends to flatten out the board and will give speed.

hope that made sense....