The penalty becomes -100% for Ecologist-led Democracy/Federation, -75% for Ecologist-led Dictatorship or Republic, and -50% for every other leading party.

<Property Name="PlanetInitialFIDSPenalty" BaseValue="-0.5" MinValue="Negative"/>

SimulationDescriptors[LawEffects].xml

<SimulationDescriptor Name="LawEffectP04L00" Type="LawEffect"> 

<Modifier TargetProperty="PlanetInitialFIDSPenalty" Operation="Addition" Value="-0.5" Path="../ClassEmpire/ClassColonizedStarSystem/ClassColonizedPlanet" TooltipHidden="true"/>  

<Modifier TargetProperty="DemocracyLawsDiversityHasEcologist" Operation="Addition" Value="1" Path="../ClassEmpire" TooltipHidden="true"/>  

</SimulationDescriptor>

<SimulationDescriptor Name="LawEffectP04L00Republic" Type="LawEffect">  

<Modifier TargetProperty="PlanetInitialFIDSPenalty" Operation="Addition" Value="-0.25" Path="../ClassEmpire/ClassColonizedStarSystem/ClassColonizedPlanet" TooltipHidden="true"/>

</SimulationDescriptor>

<SimulationDescriptor Name="LawEffectP04L00Dictatorship" Type="LawEffect">

<Modifier TargetProperty="PlanetInitialFIDSPenalty" Operation="Addition" Value="-0.25" Path="../ClassEmpire/ClassColonizedStarSystem/ClassColonizedPlanet" TooltipHidden="true"/>

<Modifier TargetProperty="Happiness" Operation="Addition" Value="15" Path="../ClassEmpire/ClassColonizedStarSystem"/>

</SimulationDescriptor>

I investigated and playtested it, is indeed an issue.

Is also present on SimulationDescriptors[LawEffect_DLC2].xml, on "LawEffectP04L00DictatorshipMajorHisshos".

Can be solved easily using Operation="Maximum" instead of Operation="Addition".

Another option is to remove the modifier from "LawEffectP04L00", as it is not needed, and change the sign on the variants.

Both solutions are fine, tested both, the modifier is hidden and later overwritten for GUI Law description.

There are these current possible alterations of "PlanetInitialFIDSPenalty":

Initial value on planets is "-0.5".

Is forced to "0", when:

Planet is unique.

Empire is Minor Faction of Academy

From faction Gameplay Affinity: usually added to Tier 1 planets, Terran, Ocean, etc, with the exception of Riftborn that does it with Sterile Planets.

You have the technology for that planet colonization (including Gas, as it was fixed earlier).

Is modified only by "Hardship Ready" law and the Republic, Dictatorship and Hissho variants.

Adding a Maximum Operator plays nicely even with Force (force should lock the value but not 100% sure), no matter the order of modification of the planet property.