Great, working as expected now.
There is a slight bug however, not sure if it's browser related but if you quickly hover in out of sprite the opacity value sometimes will only reverse to 50% of the initial value, it's like the initial value is getting reset at mouse out . It seems to be stable for everything else like height/width etc.
I will have a bit more time to test things in the next few evenings so will report back if I find anything else. Thank's again for this.