@Jose
you are right, the examples in the HRM are only meant to illustrate concepts, they are not working programs.
There are also unprecise stuff, or confused one.
This is what I remember (i have no code to check at the moment)
The values you write in the DFFSTxx registers are horizontal position bits starting from the second-least significant bit H1 (the least significant is H0 and is not present in DFFSTxx but it is present in DIWSTxx).
So in this sense the data fetch has a "2 pixel resolution".
However, the least significant bit of the REGISTERS DFFSTxx
although existing cannot be set to 1. You can see this in the appendix, where the register bit are explained: you will discover that in the bit position 0 there is an"x", meaning that the bit is always 0 regardless of what you write into it. So, in this sense, they have a 4 pixel resolution.
So why the bit H1 exists in the registers even though it cannot be modified? Only Jay Miner knows!!! :-)