Flower Gift rises Attack and Special Defense by 1.5x. I'm fairly certain of this, I just haven't had a chance to get some hard numbers.
Lvl 25 59 SpA Cherrim Magical Leaf on Lvl 14 31 SpD/51 HP Starmie.
No flower Gift should yield 19 - 22 damage.
Test 1: 51 (OHKO)
Test 2: 51 (OHKO)
Test 3: 50
Unless I'm missing something, Cherrim's SpA has to be at least ~ 137 - 166, which is a ~2.3x - 2.8x boost. This is ignoring a possible SpDef boost via Flower Gift.
You screwed up the damage calculation. Assuming no boosts, the damage range is 72-86. Assuming a 1.5x SpDef boost, its 50-60. You data falls in the range.
Lvl 25 59 SpA Cherrim Magical Leaf on Lvl 17 45 SpD/123 HP Chansey.
No Flower Gift should yield 13 - 16 damage.
Test 1: 19
Test 2: 18
Test 3: 18
Test 4: 18
Test 5: 19
Magical Leaf would deal more damage with the 137 - 166 SpA, at least 29 -34, which indicates that Chansey's SpDef was boosted through Flower Gift.
Damage range without SpDef boost is 25-30. With the boost 16-21. Your data falls in that range.