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?