I will write what he meant in as plain english as I can manage...
Emmanuel wrote:
not only terain but smoke too
no my mod is designed on this=all units are builders
but i understand what for all mapper give a 1000hardness
so in 3years you think diferent about hardness when your hardwar will be suficient
me i lower the detail for hav nomany lag and that work with 100eplod in screen(not nuc explod)
Forboding Translation:
Not only are there large explosions in my mod, there is a lot of smake as well.
My mod is designed upon the premise/principle that all the unts have some building capacity.
I understand the reason that all mappers give a high hardness value for maps.
In 3 years when hardware is more advanced/more powerful you won't be as concerned

Personally I lower the detail settings and get only nominal/marginal lag when there are a LOT of explosions going on.
You have a good point about the hardware. Another thing I should have mentioned is that I don't think that terrain deformation is quite so laggy in the new map format.
BTW I think that the premise (Foundation) of your mod is quite interesting. Whether I enjoy it is a different story, but I'm definately looking forward to trying it out.
BTW to answer your original question: I do not believe that gravity affects/effects terrain deformation. I could be mistaken, but I'm about 90% sure that gravity takes no effect.
A good test for you would be to set the map hardness to something like 70, and put the gravity at 160, blow a hole in the ground. After that, set the hardness to 70 and then put the gravity at 30. Then just compare the holes and see if they are different. Make sure you use the same weapon for the hole.