More to the topic, I don't necessarily think that research into sex itself is entirely going to help with ecchi. Most of the Kama Sutra consists of cultural (and possibly slightly outdated) expectations and suggestions for "proper" social courting of a partner. I have to say that some of the suggestions are actually helpful for marathon sexing, and I appreciate the focus on intimacy in that regard. It can be good for idea generation, of course, and some interesting art reference if you're into that. I might take from it eventually, if my friends don't ban me from looking at it again; There are actually some dubiously magical connotations for where to focus energy and whatnot, and my friends have collectively decided that I should never practice sex magic after what shall only be known as that incident.
Anyway, less about sex, more about sexual implications. Ecchi's primary focus is to gently arouse, to tease, and to allow the viewer to have more of a window than the MC in most cases (as far as I've observed). Most of this is typically achieved through humor and situational irony. It's exaggerated, and the line that makes it so hard to walk is that it's a constant balancing act of all these different forces, especially suspension of disbelief. Let's be real: there's a lot of bad ecchi that does not accomplish this well. Some of the more successful ones I've seen have a primary plot that has nothing to do with the perverse persuasion going on in the background.
I think, therefore, ecchi is more about the approach. It's hard to work with it if you have that mindset of hardcore versus softcore porn, because ecchi isn't really about the sex--sort of, but not really. Typically the series ends more or less with the MC hooking up with the chick that he was obviously going to get with from the beginning. That means that the story's actual content is all about the context and the buildup, and that's what makes it so attractive to some people. It's very similar to the mentality behind why fishnets and lingerie are considered sexually attractive. It allows for the playfulness in the sexual tension, and that starts on the path for the lightheartedness that makes ecchi what it is. I hope that makes sense.
((Also I totally added that quote to my signature because it's too perfect.))