The trials were against a very tight deadline, so they tested the minimum time. They haven’t been even been able to test the maximum deadline, so anything about that is just conjecture.
The Government extended the gap between the 1st and 2nd jab, and it has turned out to be a fortunous guess.
The gap does not have to be 2 weeks, it can be longer.
To cut a long story short, whacking in as many possible millions of jabs in, as quickly as possible is the best option. Following up with the second jab at a later date is a very minus bonus. As little as 4% over the the entire course.