For those who want to know, here are the figures for Raid Boss drop rates taken from the Japanese Info.
I have only done figures for Mid-Grade seeds. Thanks to Nikonana for the link to the info.

Boss List and Reward

lvl 41 = 20 lvl 51 = 37
lvl 42 = 22 lvl 52 = 40
lvl 43 = 23 lvl 53 = 42
lvl 44 = 25 lvl 54 = 45
lvl 45 = 26 lvl 55 = 47
lvl 46 = 28 lvl 56 = 50
lvl 47 = 29 lvl 57 = 52
lvl 48 = 30 lvl 58 = 55
lvl 49 = 32 lvl 59 = 57
lvl 50 = 35 lvl 60 = 60

Boss List and Finders Fee

lvl 41 = 02 lvl 51 = 12
lvl 42 = 03 lvl 52 = 13
lvl 43 = 04 lvl 53 = 14
lvl 44 = 05 lvl 54 = 15
lvl 45 = 06 lvl 55 = 16
lvl 46 = 07 lvl 56 = 17
lvl 47 = 08 lvl 57 = 18
lvl 48 = 09 lvl 58 = 19
lvl 49 = 10 lvl 59 = 20
lvl 50 = 11 lvl 60 = 21