There were before different issues related to placement of Captcha on the form:
#765758: Don't like where captcha is placing itself on the form
#60874: position of captcha image in forms
they are about hooks and other not simple solutions

I am sure that everyone would agree that Captcha should be before submit button on any form.
So please provide some UI option to implement that.

Often users would submit without even viewing Captcha block below the form and when Captcha error is displayed, they will just quit w/o bothering themselves.