do different models yield involuntaries better?

Yes eupho moves the most, the progasm moves the least and the others move somewhat in between.That is fact by design but it depends on the users skill and muscles as to how well they can drive each model.
Glad you had your breakthrough.Involuntary contractions are the corner stone of aneros use. If you can not learn these you will get nowhere! Well done.

Thanks for the reply, I was wondering if the larger size of the progasm would cause more of these uncontrolled spasms/twitches/contractions.
It was pretty freaky when they started, and created a very intense feeling, but I felt like I was tensing up a bit too much.
Unlike what I read on the wiki, instead of doing slow contractions in and out, I simply held my PC muscle contracted for about 5 minutes. After that long holding it, I just couldn't hold any more & the involuntary twitching began.
One more thing: I found the twitching started sooo much quicker when I lubed up my nipples & stimulated them rapidly. It's like there is a direct nervous connection between them & the anus.

Thats right nipple stimulation is recommended practice.