Driving users attention through opacity masks (reading rhythm)

I was reading this handy answer about Light on dark vs. dark on light: which is better for attention span? in the Graphic Design SE site and while reading the most voted answer I discovered that my attention focus point was almost a 100% just in the top first paragraph on my screen:

I decided to make some tests on how this can apply to a user experiencing reading in a site with text driven content.

I asked the following question:

How can I control this 100% of user attention on a certain piece of text?

So I created opacity masks of different heights to visually analyse this hypothesis:

70% opacity mask height:

50% opacity mask height:

However I discovered that I experience a different 100% attention area when the text size is bigger:

So, the question is, should I use this opacity masks in my blog or site to control in a certain the user's attention throughout the reading rhythm?

UPDATE:

I think that as with large or complex forms which are tedious to complete, maybe, a user will finish a large reading if he/she gets small chunks of information instead of showing the user what's next and discover that there's a lot left to read...