I was just sat at my desk asking myself the same hindering questions, getting in my own way when I felt a sudden change in my thought process as if someone flipped a switch. 

It's all about you. Your powers are infinite and there are no boundaries unless you set them. In regards to manifesting exes and specific people, we struggle because parts of our minds will often see this as a big task and look at the obstacles and question the hows, the whys and all that hindering malarkey. Stop this. It's not really that hard of a task, it's just us putting too much thought into it because we don't see a clear path. You could manifest your ex tomorrow if you ignored your current reality. 

We're the ones who decide how "big" a desire is and how much we think about it. I could tell you now to make your intention to manifest chocolate, that'd be easy because we'd deem that as a small insignificant thing. And we'd obviously think of how many different ways it was possible to get that chocolate, you could find money and go buy a bar from a store, you could walk somewhere and a company could be giving out free samples, you could get a coupon for a free bar, in your reality I could walk up to you and give you a bar of chocolate for funsies. You wouldn't see obstacles there because there's plenty of options. Of course, when it comes to manifesting relationships with specific people/exes all we see are obstacles and trying apply logic to those will hinder us because we view it as a big task.  It's no difference between manifesting a relationship than a bar of chocolate, it's about accepting your thoughts shape your reality. 

I'm hoping this make sense, as soon as I got this thought process I scrambled to share this here. I believe in every single one of you on here, you're capable of great things and in a way I came across this forum, I've learned so much about LOA in such a short period of time.