You do not need to change the mod area at all, leave it as it is, this has no effect whatsoever on the floor height or at which point you die.

Its not the fog that kills you. What kills you is the floor height, thats the height from the bottom of the map in meters that the floor is set at. When you hit the floor levelthats where you will die. The floor level can be found in the mission file near the top and in the example below its set at 150 meters. Change this value to the height you require, which in most cases will be different for every map you make.

New MissionArea(MissionArea) { area = "-248 -256 992 512"; flightCeiling = "300"; flightCeilingRange = "20"; floor = "150"; locked = "true"; };
If you do not know how the fog works read this below as it clearly explains how to set fog levels.

General Fog

The first type of fog supported affects visibility regardless of your location. The
field fogDistance is used to determine this. Low values indicate low visibility and high
values indicate high visiblity. A value as high as or higher than visibleDistance is like
have 100% visibility (unless you have noRenderBans un-checked).

Fog Layers

As noted above, there are three layers. Layer 1, 2 and 3. Layer1 is always the
lowest and Layer 3 is always the highest. Each layer has a field fogVolumeN associated
with it. This field takes three parameters:

Visible Distance Bottom Elevation Top Elevation

The ‘visible distance’ determines the distance from the camera at which visibility
is (near) zero. ‘Bottom’ and ‘Top Elevations’ determine where the layer (or band) of fog
begins and ends respectively. To enable a band, ‘visible distance’ must be greater than 0
and ‘Top Elevation’ must be greater than ‘Bottom Elevation’. Also, do not forget, if you
are going to enable more than one layer of fog, they must not overlap each other or
rendering will get messed up. They may touch but not penetrate. Here is an example of
some settings:

FogVolume0 = “250 0 50”;
fogVolume1 = “350 50 150”;
fogVolume1 = “25 200 500”;

The first layer starts at 0 meters and stops at 50 meters, with a visible distance of
250 meters.

The second layer starts at 50 meters (touching layer one) and stops at 150 meters,
with a visible distance of 350 meters.

The third layer starts at 200 meters and stops at 500 meters, with a visible distance
of only 25 meters.

If you want more information on TGE then go to my website (click my sig to go there) and on the downloads page download and read the TGE user guide - its a must for any modder

New MissionArea(MissionArea) {
area = "-1024 -1024 2048 2048"; <------------------------------ x & y axis, surface death position preserve the ratio & use multiples of 512
flightCeiling = "1000"; <-------------------------------------- z axis, Ceiling death position
flightCeilingRange = "0"; <------------------------------------ z axis, Ceiling range
floor = "-99"; <----------------------------------------------- z axis, floor death position (-99 no kill)
locked = "false"; <--------------------------------------------