I agree with sibling comments, though, that respectfulness is not mutually exclusive with alpha-ness. And if in general you are a respectful person, a high-power posture will probably not impact their opinion of your respectfulness too much.
[1] Assuming you really want the job and unless you are a hot shot who is gracing them with your willingness to work for them.
Confidence really does work. If you sincerely believe in your abilities, it's much easier to convince others to believe in them.
[1] This is not mutually exclusive with respect or humility. It's quite possible to believe you have a lot to offer your employer while also believing they have a lot to offer you, and then the job interview process is just a matter of negotiating the right fit.
Anyway, as far as anecdotal evidence goes, I tend to intentionally give off a pretty neutral vibe and rarely worry about flunking an interview. (I chalk it up to mad skillz rather than body language though.)
The power dynamics depends a lot on the specific market conditions at a given point in time. If demand is low and supply is high, you do have a power disadvantage, but its just as possible to see the reverse where the employer is at a disadvantage.
The typical HN reader is more likely to be familiar with the latter than the former. Not because we are all hot shots, but because our industry is presently in high demand and has a low supply of labour.