HMMM. Interesting.
I have never considered the 10% to be 10% of the Hover torque for that day...Hover at 60%, T/O Power 66%...rather
Hover at 60%, T/O using 70% (Hover Q + 10%)
As a former CF flight instructor, this is the only standard I and my colleagues have used. In any case, it really is just a value to set so that new pilots (primarily) don't reef in 100%Q for every take-off they do.
Cheers.