Bay 12 Games Forum

Your magma is transported to your moat at 1 Z level higher than your moat. Thus, it will overflow. Try it with water, you'll get the exact same thing, only quicker.

You need to make all of the magma the same Z level if you want to eliminate any chance of food. Do all of the height adjustments at the source of the magma using iron pumps and windmills.

I'm almost certain that light/dark and inside/outside are identical at present - a constructed roof will not and cannot make an area 'inside' (as stupid as that sounds).

Hey, that's my fort you linked there!

I've done a few experiments with the grass and muddy floor. The grass doesn't grow just on muddy obsidian - the brown bits between the grass in my Chamber T are muddied ground and as you can see, no grass ever grows there even though it's Outside and Light. You can check that even a few years later it's still just muddy ground, no grass. There's also a little muddied channel under the bridge done exactly to check if the grass will grow.

Now if you want to drop the grass down from your soil level, it will require some planning. You'll have to channel the ground all the way around the bit you want to drop but also note that it only has to be channeled like that on the upmost level - after channeling it will just fall down where you want it.

What I'd suggest you do is channel a circle, drop it to where you want it to be and then dig your swimming pool in side that circle of grass.

Also note that aparently there's a bug somewhere that if a soil layer drops through rock layers it changes into that rock layer for the purposes of farming - but the grass will still grow on it, only no trees. It can also be used as a sand collection zone if you happen to drop a sand layer down (as mine is used).

I hope what I said makes sense 

I don't think you can drop the grass down. If you can muddy the tiles where you want it to grow and those tiles are exposed to sunlight, it'll grow on it's own in most biomes.