In answer to your second question.
Show him. This is pretty easy to do. Tickle him the way you want to be tickled, with the intro "This is the level that I want you to do to me." Or, show him a video clip that has the level of tickling you like. But a clear example, that gives him a measuring stick to work against is most important. I'd also add in that you need to talk about how important the level of the tickling is to you before play, and reinforce that you desire that.
It's possible you are coming up against a very common human response. In our culture, men are conditioned to not hurt women in any way. It's a positive message, hitting women is not cool, and being an abuser wins no points. But it has the side effect of making a segment of the male population unable to seriously do anything in the S&M world with their partners. They just can't make them selves spank, slap, be rough, cause any form of distress. Tickling seems to get lumped into this. It's a big cultural hurdle to bop over for some. So there may be a bit of this at play also.
As for the first issue, there are probably a lot of psych factors at play, as to why you become less ticklish when bound. And you might be correct about 'giving in to helplessness' and relaxing as a result. There are a few things to try that may help. I'd start with a blindfold. Simply removing your vision may do the trick. The next is what is called a 'predicament bondage' these are positions where your motion is restricted, but not in total. For example, legs are firmly tied together, but arms left free. while laying you stomach down, partner sits on your legs and works your feet. Your arms are free, but can do little. Conversely, your arms can be tied at the wrists, and he can sit with your ringed arms around him, and your head in his lap. Legs are left free. He can do anything he likes to your armpits, breasts and stomach as he has free and easy access, and you can't block it. In both cases you have a lot of freedom to struggle, but it's all pretty pointless, and he can easily control you.
Those are the simple first things I'd suggest.
Myriads