Originally Posted by IvanLedah21

I remember reading that certain buffs stack differently. Like: A+ B vs. A*B
A+B would mean 1.2 + 1.2 = 2.4
"Start with X Light Gauge" should fall into this category, I think Shine Crystals might, not sure about Attack/Defense but I'm pretty sure Skill Activation does NOT
A*B would mean 1.2 * 1.2 = 1.44
I think this is the category Skill Activation falls under.

DMM vet want to correct me, that's fine. The more accurate our info, the better for all us forum dwellers ; )

Shine Crystal drop rate is definitely of the A+B version. At least, at the start of combat, my squad with Cactace, Peach and Strawberry Candle shows "Shine drop rate 50% increased" for all members.
Moonvine + Tachibana also results in a 2.4 (A+B) skill activation rate notification on the third turn.

However, there IS something different about the effect Geranium and Cyrtanthus have: they're affected by the affection statistic. So that might be either a bug or intentional, that the second effect of the two simply overwrites the first. This is definitely something worth investigating. Still leveling Cyrtanthus here, and she hasn't even evolved yet, so it might take me till next weekend before I can really look into it.