I use the same consistency that I use to ice my cakes.
If you make your FBCT too think, it may crack. I think most FBCTs are raised. You can make a FBCT for the entire cake top to solve this problem.
Most people I do FBCT for like the fact that the image is raised off the cake some. I put a small boarder around the transfer in the same color that the cake is iced in. If you thin the icing to much the transfer will break on you. Good Luck.
I don't care for the raised effect either...so when I make them I pipe around it with the background color and just put a thin coat of icing on my cake, then put the transfer on and then ice around the transfer and let everything crust real well then go over the whole thing with a viva towel
here is a photo of a fbct I did this way...you really can't tell where it stops and starts with the rest of the icing
http://www.cakecentral.com/modules.php?name=coppermine&file=displayimage&meta=allby&uname=KHalstead&cat=0&pos=2
If you don't want the raised look I would agree with those that say to fill in around the transfer to make it the size of your cake.
When doing these they need to be around a 1/4th of an inch think. Any thinner and they thaw before you can even pull the wax paper off which can lead to tearing your piece or having it stick to the wax paper.
What about trying colorflow instead? It takes MUCH longer to dry...Like days in my case! But they are much more flat than the FBCT I have done.
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