The configuration file doesn't change the property in the game.

[Luppyn]

I'm playing on version 1.20.1, with mod version 2.0.77. In my game, I receive a warning: "Machine is too large, it may be at most 5 blocks in the x dimension". Meanwhile, in my common.toml configuration file:

Define how Reactors works

[common.reactor]

The maximum valid size of a Reactor in the Y dimension, in blocks.

Lower this if your server's players are building ginormous Reactors.

Bigger Y sizes have far less performance impact than X/Z sizes.

Range: 3 ~ 256

maxReactorHeight = 256

The maximum valid size of a Reactor in the X/Z plane, in blocks.

Lower this if your server's players are building ginormous Reactors.

Range: 3 ~ 256

maxReactorSize = 256

A multiplier for balancing Reactor power production. Stacks with powerProductionMultiplier.

Range: 0.5 ~ 100.0

reactorPowerProductionMultiplier = 1.0

[ZeroNoRyouki]

A Basic Reactor has a fixed max size of 5x5x5.