Act like a pollinator and visit regularly to catch all the different phases in the action. Bigger cyathia are easier than smaller ones to sex. And I find close up pictures incredibly helpful in sorting these things out, relative to the in person experience alone.
For all Euphorbiaphiles in the group, I recommend spending some time on this site
https://www.euphorbia.de/index...
which was not operational last I visited, but seems to be back. For example this entry:
https://www.euphorbia.de/e_knu...
For a lot of plants they indicate self fertility or self sterility where relevant. There's a whole detailed key relating to cyathia. More than you probably wanted to know.
