Have a look at the picture of the white chocolate shoe on the cake IMG_3278 I did at this wedding.
http://www.lucidcreations.co.uk/wedding/ (sorry the web space is a bit slow).
I was about 1m away from the cake and it was shot on f1.8 in error, but you can see what I mean about the your shot being about right. BTW these are just proofs.