The "thobbing" that i feel is the penis contracting and twitching (I guess )when it is cuming. More the movement the cock itself makes when it is cumming .
I can definately feel my husbands head swell up before he comes, ( his cock head is big with really pronounced ridges and gets REALY big just before he comes....I can always tell when he is going to cum as he sometimes hurts menwhen he drags it in and out fast.)
I tried last night to hold still and see if I could feel the liquid actually shoot out, alas no go.
Hubby shoots an average amount but not that far, like when we are fucking missonary and he pullsbout, it will hit my neck and chest....maybe bigger cummers you might feel the actual ejaculation more ?
( we always use rubber with other men so I have no idea )