I don't see a recommended flavor percent on their page, am I missing something?
The recommended flavor % is usually posted when they list a new one, like for the Succulent Strawberry which showed the 5-10%, and maybe still does. I haven't checked lately.
The usual range Kim (OSDIY owner) recommends for the OSF and OSB, when used singly, is between 5-10%. She said around 10% would probably be best for tootle puffers and about 5% to start with for those who vape higher wattages.
For me, the % I use depends on how strong/potent the flavoring itself is to me. For most, I use them singly at between 7-10%. For the Succulent Strawberry and the Blueberry though (which are both very potent), I start now at 3% and work my way up if it's necessary after several days. I've found that both of those seem to get stronger after about 3-4 days.
For some friends that I make a few of them for, the flavoring % they prefer
seems to be related to the nic mg they vape at though, rather than what wattage. Both of them are tootle puffers. One vapes 12mg nic and likes her Lucky Shot + Lotta Latte combo at 7% of each. Another vapes 15-18mg nic and likes hers at 9% Lucky Shot + 8% Lotta Latte.
So I'd start with most at about 5-6 and work your way up if necessary. You can always add more in a couple days, but can't take it out. The Succulent Strawberry and the Blueberry though, I'd start even lower with them and wait at least 3-4 days to see how they are. 2 local DIYers I've given samples of those to, both sub-ohm vape at about 40-60W, and their eliquid is 3mg nic. They like them at 3-4%.