Ok, YAY! talia got it......it was a classic set up and punch line...
echoes, in My experience, and I can only speak for Myself, the more excited I am mentally, and looking forward cumming, the more I'll cum at once, volume wise I'm speaking.
Now I'll say its very difficult to pinpoint any differences, in the source of the contractions, as it seems they all begin in the lower abdominal area and extend into the pc muscle therefore causing the entire shaft, anus and stomach to contract and give the pleasure an orgasm creates.
I will say, the more excited I am the first several contractions last longer in between 'spurts', becoming almost a 'locked up' feeling at those most intense times.
Let me add, I am so very jealous that you girls have so many souces and different types of orgasms......I wont even mention that you can have 1 to 30 a session....stomps foot...NOT FAIR!