Hello OrmIrian
Just thought I'd say that how you feel now running 9 miles is the same as running 16 miles except for the last bit.
For me the first 3 miles are always hard, I get little niggling thoughts like "What are you doing, I dont feel like running today.. etc" Like a rusty engine getting going.
At this point I start a chant in my head like
"I feel good, I feel strong, I can keep running on and on"... or whatver and then I lose some time.
I also read its very important to not always distract your mind with other thoughts which does help but to actually encourage your mind to enjoy feeling your body running, your feet pounding, your breath, looking up and not a couple of feet infront all the time. This is help with longer runs.
I have to say no matter how many miles I run the last is always the hard, 3,5,9,10 or 17 the last mile is the killer and like I you I think its in the mind! This long run when I was a couple of miles away I started imagining my family friends were scattered along the roads cheering on and imagined I was approaching the finish line of the marathon. I actually ran faster as I came near my house it helped so you could try that.
You also asked how to lengthen the feeling you get in the middle otherwise known as the "flow" I come in and out of the flow throughout my long runs and not sure how to advise you on it. But I do not that I tend to enter just after points where I am not crossing lots of roads and I am thinking positive thoughts and chanting encouraging words. Usually around 12 miles I start to feel aches and pains but I always tell myself "Whatever you are feeling now, you will feel at 16 miles, it will be no worse, so just relax and let it happen and you will cope with it" I start doing this on my last few runs and instead of tensing up when the aches came, I accepted them and they disapeared and returned a few times. In my book, its says when you feel pain say to it "Hello pain, wont you run with me?" sounds weird but it works for me.
You are doing great, every week when my miles increased and I ran the longest I ever ran I was so proud of myself and so should you. Last year I could not run for 5 mins and this Sunday I will run 3 hours. Its not magic, our bodies are capable of so much. This marathon training has really shown me you can do whatever you want with hard work.
Good luck!!!!