You don't need to worry about the 'adjustment' bit. The male penis has hundreds of senstivie nearve ends, it is the touch and stimulation of these that gives your partner pleasure. Because various nerve ends cravev stimulation at different times, and with different intensity, your partner will adjust his position intinctively in aswer to these nerve messages. It is perfectly normal, and nothing for you to worry about. The idea that you are not tight enough is probably unfounded - it is in fact an excecllent sign that you are relaxed and lubricated enough to enjoy sex easily - the reverse of the most common problem women experience. In respect of your partner's ejaculation, again nothing to worry about. The nerves in your vagina again respond differently, with varying sensitivity - some will actually fail to register the additional impact of semen, given that you are already well lubricated and relaxed. DSome women feel it, some don't, it can vary with the partner, and the strength of his ejaculation, but if your partner has no complaints, then don't owry about it. As you say, this is a matter of experience, but is sounds like you are getting all the important parts right, so go with the flow (pardon the pun!) and enjoy it.