Preparedness centers are supposed increase planetary defense by 50%, but the numbers are weird. If I build one next to my colony capital, I get 15% defense (10% from adjacency plus 50%). If I build in a military 3 (caverns) tile, I get 45% - 30% from the level 3, plus 50% from the center.
I think that most of these bonuses are supposed be additive not multiplicative. 50% + 30% for level 3 (80%) not 30% (lvl 3) plus 50% of 30%.
Not sure where Shielded (25%) fits in. Currently it multiplies: 30% plus 30% times (50% + 25%)
Even if it was multiplicative, it should probably be (50% + 10%/level) times base, not 150% times (level x 10%).
Even the planetary defense system is +25%. 25% of what?