I don't know if you can, or are interested in doing this, but I thought I would make the suggestion of having Factorissimo's factories push the upgrades on their floors if they are built underground. i.e., if a factory is built on underground 2 everything gets 10% productivity within the factory.

Again, I don't know if you can, or if notnotmellon would have to program this, but I wanted to make the suggestion since I've tested how the two interact - a new surface is generated if a factory is built underground, but the bonuses (and minuses) do not apply. I would think it should be possible since the factories are influenced by the surface they are placed on, but I don't know for sure.

On an unrelated note, how large of a cavern does one have to dig to cause a cave-in?

That should be something for notnotmelon - just copy all surface effects

Cave-ins are not yet implemented

I agree, but I kind of doubt that they will do it, so I thought I would suggest it here.

Anyway, if cave-ins aren't implemented yet, please - for our sanity - provide some kind of warning in-game before it applies. I'm sure I'm not the only one who has/will have large carved-out areas.

Thanks for the lovely mod, keep up the excelent work.

i do remember seeing someone talk about working on adding surface effect coping to factorisimo in the factorio discord, looks like one of the problems with implementing it is there is no automatic way to disable recipes that are no longer craftable if you move the factory to a surface they cannot be crafted on built into the game, so that would have to be handled with a script

I should really join the Factorissimo discord for this, but I don't like expanding my, uh, visibility(?) that way (I'm a "lurker" most of the time, you see...)

Shouldn't surface-level recipes be craftable on their subsequent sub-surfaces? I.e., shouldn't the science packs of the other planets be craftable on the subsurfaces of those planets?
If the answer is yes, then Factorissimo's problem is handled because you cannot transport them via rocket. So they would only be able to be built on the subsurface of each planet - which should be able to handle the recipes of that planet anyway.

The thing that would break this is a mod that would allow bypassing the rocket for travel, but that would break Factorissimo anyway if its surface calculations work the way I think it does (i.e., the world they are built on sets their surface conditions?)

I may join the Discord just to post this point.