With RI I only get tones above high C. I cannot play lower in this setting.I like this, but how do I proceed and is it OK?

It is great fun the first time it happens. BTW If it doesn't happen it is OK, too. My advice would be to always go for the G top staff. If this tone is really 'too low' in the beginning, a high C is also a good starting point.E top staff is the lowest starting point.The exercise is meant to gain control over this extreme set up.If you try to make high E your starting point, the risk of forcing is high. If you get tired (and you will) high E is a high note even RI. If you still want to use this as your starting point, eventually you are going to force it and miss the point. Merely trying to find and play a G top staff is a great workout and makes your lips eventually do the right thing. It may take a while but it is a great coordination exercise.