The minimum standard was set this time last year and is has not changed since then. The requirement is that 60% of pupils achieve level 4 in English and maths by the age of 11 and at least an average level of progress between the age of 7 and 11. I don't see that as an unfathomable formula, or are you referring to CVA - I would agree that is unfathomable.
There are roughly 200 schools that have failed to achieve the minimum standard for 5 years or more.
I presume from what you are saying that your school is in the next tier up. There are 500 schools that have fallen below the minimum standard for three or four of the last five years.
The initial intention was simply to ask the LAs to draw up plans for improving them. However, the data revealed that 9 LAs had particularly high concentrations of the worst 700 schools. Between 100 and 200 of the schools are in just 9 LAs, each of which has over 10 of these schools. The remaining 500 or so underperforming schools are spread across over 120 LAs. The underperforming schools in these 9 LAs are coming under intense pressure. However, they will not be forced to convert if they can demonstrate an upwards trajectory at KS2 and/or participation in a successful federation of schools.
By the way, the data shows that if you go back 3 or 4 years you will find that the same 9 LAs had high concentrations of the poorest schools and, by and large, it was the same schools.
So your LA has not been targeted at random. It has been targeted because it has a particularly high concentration of underperforming primary schools.
I am not saying that converting these schools to academies is the correct course of action. I don't know whether or not it will produce the desired improvement in standards.