Does not work.
<GlobalCombatMods>
<EffectType>Maintenance</EffectType>
<Scope>Global</Scope>
<Target>
<TargetType>Ship</TargetType>
<TargetQualifier>IsStationed</TargetQualifier>
</Target>
<BonusType>Multiplier</BonusType>
<Value>-0.50</Value>
</GlobalCombatMods>
If I change it to:
<GlobalFactionMods>
<EffectType>Maintenance</EffectType>
<Scope>Global</Scope>
<Target>
<TargetType>Ship</TargetType>
<TargetQualifier>IsStationed</TargetQualifier>
</Target>
<BonusType>Multiplier</BonusType>
<Value>-0.50</Value>
</GlobalFactionMods>
It works.
Scratch that, must have been the loss of constructors to Starbases that reduced my maintenance 