HFO without much ejaculate

I am just beginning to use my progasm and had an interesting experience on about my third time. While the progasm is inserted, i lightly stroked my cock and could feel the sensations in my rear begin. After a bit, i stopped touching myself and let the aneros take over.

Squeezing and releasing, I finally had a great orgasm. My cock was immensely hard and very very dark. It looked like it was going to burst! But the feeling was wonderful. I kept on the edge of release for a while then finally couldn't take it, and had an orgasm. It was much deeper and stronger than any I have ever had. There was very little semen ejaculated, only one big drop. Is this a normal amount of cum? Am I on to learning how to use this the right way?