It’s good to know that you got it working by tweaking it but you really shouldn’t have to do any tweaking. I don’t know exactly what you did for your specific wordpress setup but I suspect some steps might be missing. I have a few customers who installed thier wordpress in a sub-directory then used redirection to access it from the root domain.
The changes you did shouldn’t break anything else but it can be limiting as you are specifically posting to a page.
action="" means post to the current page (whatever this page maybe)