If the universe was fine tuned for our life...

[Jenny A]

A sub reality is a space continuum that is governed by rules. The space continuum of a subreality is not the space continuum of its parent reality.

Space is a dimensional extant where things happen. By dimensional I mean the space has dimensions. In our reality it has 3 spatial dimensions and 1 time dimension(as far as we know). Continuum refers to continuity. It isn't broken up into chunks.

A sub-reality is not equivalent to the actual reality because a sub reality is dependent upon another reality. Actual reality is not dependent on anything. Actual reality by definition is all there is. The two things, actual reality and sub reality are very different from each other.

So to put it all together, a sub-reality is an existing undivided dimensional space governed by rules other than those of our reality?

Either that definition is overly broad, or there are none. Let's start with overly broad. Have you ever played classic non-computer aided D&D? Words and graph paper describe the space and the rules for the space. Although rather more primitively depicted, it is every bit as much a space as the graphics in a computer game. There are rules governing that space which are primarily those of chance. To determine what happens in the space we roll dice of various numbers of sides.

Many war games played with cards and boards are similar. At the simplest level so is chess. All of them have a depiction of dimensional space with rules for operating within the space. Other than the artfulness with which they are depicted and the speed at which the rules can be calculated, these spaces fit your definition every bit as much as a computer game space.

Here's the rub. They aren't really extant. The spaces of these sub-realities don't really exist. They are just imaginary spaces depicted with more or less ingenuity. Consequently, I don't think they are nearly enough like reality to tell us anything about how reality was constructed.