Just a guess (I'm not the previous user), but I guess you need to look at the space _per GWh_?

If a big nuclear reactor takes 10x more space but has 20x more capacity, then it means not having much space favors the big nuclear reactor rather than building 10 small ones that will take twice more space.

(and same for the time)

its probably my fault for not making myself clear. i mean when the available space is constrained to a specific amount of space that cannot be exceeded.

just picking random numbers:

i have 1 square mile available. a big reactor takes 4 square miles. i cannot fit a big reactor, despite the bigger reactor being more efficient.