It will definately affect the nature of the technique, though all of the same techniques can be done...the amount of reaction time to learning the path of the strike as well. I personally prefer starting yokomenuchi from the forehead, and I am most familiar with that method. I have seen others...for what those instructors wish to accomplish, I assume it does just fine.
I agree with Ron. I do it his way now. I did learn it the other way at first, but coming from the forehead is more in line with a sword cut.