Believe me, a very rare number of people on this forum has really a clear idea about NOC and job duties.
CIC have never said about "Percentage" of job duties specified in the said NOC. In my opinion it's all a myth, perhaps some would disagree.
I'd like to pin here the official statement given by IRCC on their website. Here it is.
http://www.cic.gc.ca/english/resources/tools/perm/econ/fsw/minimum.asp
In continuation with the 'Minimum work experience requirement', they say,
"
In addition, during that period of employment, the applicant must have
- performed the actions described in the lead statement for the occupation as set out in the occupational description of the NOC [R75(2)(b)]; and
- performed a substantial number of the main duties, including all of the essential duties, of the occupation as set out in the occupational description of the NOC [R75(2)(c)]."
So, what I infer from this statement is that if you have performed almost all the essential duties and the great number of the main duties, then you are good to go ahead. You fulfil the minimum requirement. It doesn't have to be stringent with 'Percentage'.
And, as far as the percentage is concerned, some might consider 80% as being 'Substantial', whereas others might say 60 - 70% as substantial. It's all subjective.
To conclude, it's IRCC who takes the final decision on this. Let them take it. And be relaxed and enjoy this eagerly waiting time. This time won't come again in your life. Just live it full on. After all, you already have submitted and can't do anything about it now, can you?
Just chill.
All the best with your app.