some terms you should know:
the stock valve seat (on the cylinder head) has 3 individual or "discreet" concentric angles: 30-45-60 degrees.
The end closest to the piston or combustion chamber side is called the "top cut" at 30 degrees.
The middle 45 degree angle is the actual seat itself and lines up to the 45 degree angle on the valve face's seat (on the valveface, the portion above the seat is called the "back cut" and the portion below the seat which is just a rim is called the "margin").
The angle at the end closest to the IM side or intake port opening is called the "throat cut" at 60 degrees.
So in terms of points of reference when someone says a seat angle is "above" or "upper" or "higher" they are referring to the top cut side of the seat angle proper...
whereas the angles "below" or "under" or "lower" to the seat angle proper is the troat cut side.
5 angle valve jobs involve adding 2 more discreet angles to the valve seat on the throat cut side.
the "bowl area" of the port is towards the IM side of the valve seat from the outside of the valve guide down to the short turn radius or floor of the port at the downturn bend to the throat of the combustion chamber.
The last angle on the throat cut side is "blended" or ground so that it flows smoothly and continuously into the port bowl area...you hear the term "bowl blending" by headporters and this is what they are referring to.
To answer your question about the b16a vs itr head difference:
The valve job done on the ITR head intake side (ie. the side with the larger valveface diameter when you view the combustion chamber in the pic) is what makes it special compared to the b16a head.
The 3 angle valvejob is redone at the factory by hand on the ITR head by selected trained porters at Honda in the Suzuka factory.
The throat cut seat angle is reduced from 60 to 45 degrees on the ITR head and there is a significant amount of bowl work and bowl blending...the result is more high valve lift flow...and more flow in the upper rpm powerband.
you may want to read the valve seat angle tech article...I don't get many questions about that article as it is.