I'm not an expert, but I shall endeavor.
In your params should be this:
[CAVERN_LAYER_COUNT:3]
...
[HAVE_BOTTOM_LAYER_1:1]
[HAVE_BOTTOM_LAYER_2:1]
[LEVELS_ABOVE_GROUND:15]
[LEVELS_ABOVE_LAYER_1:5]
[LEVELS_ABOVE_LAYER_2:1]
[LEVELS_ABOVE_LAYER_3:1]
[LEVELS_ABOVE_LAYER_4:1]
[LEVELS_ABOVE_LAYER_5:2]
[LEVELS_AT_BOTTOM:1]
HAVE_BOTTOM_LAYER_1 is the magma sea, you can turn it off. HAVE_BOTTOM_LAYER_2 is the circus and if turned on will force the magma sea anyway. The cavern number is self-explanitory. Levels above ground is how many z-levels extend above the surface. LEVELS_ABOVE_LAYER_1 is the number of levels above the first cavern; ie. the number of z-levels between the surface and the first cavern. LEVELS_ABOVE_LAYER_2, _3, etc. are then apparent and will define how many z-levels are between the 1st and 2nd cavern, 2nd and 3rd, etc. The last, I believe, is the number of levels occupied by the circus.
Be careful turning off caverns completely. This will mean that no civilization will discover underground crops and you won't be able to grow a single plump helmet.