First of all, thanks for the great game, ty for allowing flatten paved cells.
Terraforming seems to me like a core feature of the game, I love creating eeries and imposing fortress in top of the mountains. But multiple bugs make this ridiculously hard, or even impossible.
Most of it was discovered after multiple and precise experiments, read it carefully as it sometimes requires some imagination.
First: I just found out that if cobble flow at 1.5m, dirt at 2m, paved at 4m ... the Rock ! (hard solid rocks, the things you can't terraform, only mine) flow at 10 m !!! This is ridiculous! Whyyyy ? There are stiff cliff with 50 m of differences.
Second: If for whatever reason, you have a cell with impossible elevation (dirt with one of 8 cell at 3 m bellow, or rocks (!!!) at a cell at 11m bellow) it will block ALL the cells bellow (in triangle) from being terraformed. It makes no sense, I understand that the cell with bad elevation should be blocked unless it is lowered, but whyy disallow to elevate all the cells near. It should flow as expected if you lower a cell bellow also (it do it some time, not other, didn't found the logic). You can fix it if you found the broken cell and it is dirt, if it is rock ... you are fucked.
Third: If you mine 1m hight of rock, and let it collapse and transform to dirt, you will need to extract 30 stone of dirt in order to lower by 0.1 m, just as expected. But ! If you mine 2m of stone, you need to extract 60 stone of dirt in order to lower by 0.1. If you mine 4m (the maximum possible) you will need to excavate an astonishing 120 stone of dirt to lower by 0.1 m! and you need to do this 40 time! 4800 stone in total in place of 1200. You are violating the law of conservation of matter! Some call this "freezed dirt". And it is a pain in the ass.
Third-bis: I don t see why we dont have an action "Make this tunnel collapse", It was crearly possible at the time to make tunnel collapse, you didn't just sit down and waited 2 weeks (game time) for it to collapse naturally. It should be an action like anything else.
Fourth: At first, clay has a flow hight at 4m, you used for building 8m hight walls. It was ok as clay is hard to found. Now you use paving, but you can't pave on pave. So you need to make a huge pile of dirt, pave the top, then take the dirt back. it is tedious but ok. The problematic thing is that it is a very punishing practice. Because if you happen to lower the paving, you create a bugged cell with dirt higher that it should be permited. And if you lower it by mistake again, you are fucked. You will be unable to get it back to it level, unless you recreate the huge slope. Wich is Not Possible if you have builded bellow, unless you destroy every building ... verry punishing indeed. A fix will be to allow to pave on paved, limited to the current 4m (wich is dubious maybe in term of realism, but maybe it was done like this), Or you could create like concassed dirt (who will require like 60 stone of dirt to create concassed dirt that you pull by 60 stone to elevate by 0.1m) it was actually done for example in Qin dynasty 200 BCE to create their huge emperor pyramidal mini mountains burials.
Thanks for your time.