Yeah, pretty much the same, at first i stopped 3* at maps 8 or 9. Then i started using my leftover stamina for some tries to 3* them eventually, also, because i wanteed the gems for limited 2. And for maps 11 and 12 i just farmed them for the garden untili got the 3 stars.
I'm still missing 12-5 due to lacking a tiny bit of power to 3* reliably (i could bruto force it until all goes well though), and 10-5, becaue 10-5 isa rel pain and 50 stamina gardens suck.
By the way, may i know how are you calculating those 0.78% odds ? As far as my calculations go, you need to win 4 coin flips in a row, so that should be 1/16, or in other words, a 6.25%. Still pretty darn low though