You might be expecting too much comprehension in the first steps of the process. Save the more detailed reading for Rapid Reading. Continually remind yourself to only seek information relevant to your purpose. Avoid reading the superfluous text. You might like the strategy on page 71 in the 4th edition PhotoReading book "Take the five-day" test. It is great for allowing more incubation time & automatic activation. You might be more confident at the end of the 5 days that you are in command of the information you need.
Enjoy PhotoReading!
Patrick