Sorry for the late reply, we haven't played 7 days since last time (holidays and stuff) and we finally got together yesterday only to find the changes he did on the biomes.xml did not work (changing fog min-max of the biomes to 0), like you mentioned above it's a host setting (I assumed it would work since in my modding experience it always affected client side) afterwards I tried to change mine and it did not work for some reason.
After looking around the files I found fog settings in worldglobal.xml, after messing around with it, I accidentally deleted the fog for everyone and my 2 other friends complained that they liked it better with the fog.
Once the gaming session was over, I went and played with the settings for an hour.
Here's my final worldglobal.xml file, the fog setting I played with was "fogPower"
<?xml version="1.0" encoding="UTF-8"?>
<!-- Defines global world information -->
<worldglobal>
<environment>
<!-- day, night -->
<property name="ambientEquatorScale" value=".7, .45"/>
<property name="ambientGroundScale" value=".3, .05"/>
<property name="ambientSkyScale" value="1, 1"/>
<property name="ambientSkyDesat" value=".95, .7"/>
<property name="ambientMoon" value=".9, .3"/><!-- add, scale -->
<property name="ambientInsideSpeed" value=".3"/>
<property name="ambientInsideThreshold" value=".2"/>
<property name="ambientInsideEquatorScale" value=".5"/>
<property name="ambientInsideGroundScale" value=".4"/>
<property name="ambientInsideSkyScale" value=".7"/>
<property name="fogPower" value="1.5, 1.5"/> <!-- day, night -->
<property name="fogWater" value=".47, .2"/> <!-- density, speed -->
<property name="fogWaterColor" value=".38, .42, .38"/>
<property name="test" value="1"/>
</environment>
</worldglobal>
The value inside the "fogPower" works in reverse with a maximum value of 2. Meaning "0, 0" = Full fog (you can't see 2 inches in front of you), "1, 1" = Normal, "2, 2" (and above) = No fog. I put it to 1.5 and as a result our game has half the normal fog.
I know it affects everyone in the server since I'd first set it to 10 thinking it would give 1/10 fog but just deleted it.
All that happened pretty quickly, which is why I didn't have time to test your modlet @BFT2020 before coming back here, sorry for that.