You're right, I confused myself by calculating total avg yield and comparing it to yield per harvest (and you're right, A19 would be infinite so I'm basically comparing apples and oranges).
Isn't the math a bit off though? 50% chance of getting 4 crops before running out of seeds, 25% chance of getting 8 crops before running out, 12.5% of getting 12 crops and so on (6.25% chance for 16, 3.125% chance for 20, 1.5625% chance for 24) ultimately averaging out to a yield of 8 crops...