Weird thing is, another cutting about the same size from the same tree that I planted in the ground looks very week and hardly grew compared to the one pictured that I have had in a pot. I think they really need to sit in water.
Fill the styro cup slowly with soil, over days and when filled like a pot. Punch holes, then just water like a normal pot.
This how a friend taught me to grow avocado seeds, with toothpicks as supports, base of avocado, sitting in the water.
Good Day
Anthony