As long as you remember the basic rules of how power generators work, you should only be a few ships away from being able to eyeball and guess the best way to place reactors in just about any shape of vessel without needing complex math or standardized designs... Although standardized designs are just as viable if every vessel you need to fit one can.
Here's the basic rules of setting up efficient power generators, mathematical complexities not included:
Each power block gives a base 25 energy regeneration per second, no matter what.
Power blocks receive bonus regeneration based on the total x, y, and z dimensions of a group added up. This is usually called the boxdim bonus.
A 'group' of power blocks is any set of power blocks connected by touching faces.
Once your bonus regen from boxdim bonuses hits 1,000,000 you no longer receive any boxdim bonuses for additional power blocks, instead just getting the base 25. This usually happens at the 1.2 million regen mark, as the base 25/block regen accounts for the extra 0.2 million regen.
There's plenty of other quirks about how power is calculated and it's calculation rate that one can figure out with some practice and experimentation.