Yes, I feel very comfortable pulling big guys into me - particularly where I am inside the defenses. In my years of sparring before the protective equipment days, I often got the $hit beat out of me when in striking range. I rather like getting so close to a big guy that they can't hurt me. It was my only way of handling several fighters whose names I still remember today because of their rib-cracking and jaw breaking power.
Look at it this way, Dana. You stopped the sequence at the knee movement. What comes next? A cupped hand movement that works quite well as a groin strike. So I go to the face/neck, then the midsection, and then the groin. It's all done as a single movement in my kata flow; I have chosen to parse the sequence in a way different from yours. (With absolutely no claim of a superior point of view) Going to the groin twice seems redundant to me, unless I wanted to ring the bells one at a time...

Yes, your knee strike works beautifully, and you should keep doing it. Yes, I like it. No, it's not my favorite application of that technique - particularly because this is the only place in Seisan or any other Uechi kata where you can be doing a knee thrust as opposed to a knee strike. The mechanics of doing the two motions are very, very different. I like having both in my bag of tricks.
Actually hitting the testicles (as opposed to any other landmark in the groin area) is harder than you think, Dana. Their position can vary from person to person, and even vary within a person depending on body temperature. John Carria was pointing this out to me once, w.r.t. the takedown in dan kumite. He made me stomp down hard on him to prove a point. Yes, he has cahones... (I've seen his kids

I would prefer a lifting leg motion, like trying to kick a 50 yard field goal. My toes would be sticking out the back end of his leg "V" while lifting his body over the goal posts.

Oh, and after the cupped hand strike to the groin - which makes them bend forward in pain - what about doing that circle "block" that you omitted?

- Bill