Need help placing a second subwoofer.

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But by what I'm hearing, the main sub shouldn't be front and center like mine is, but closer to the main speakers and probably lightly forward because of time delays of the lowest frequencies, is this correct? 

Correct in the sense that is what you are hearing from people, but incorrect in the sense it is wrong.  

Subs put out low bass. Low bass is very long wavelength. So low we don't even hear it until one cycle. So long by the time we hear it the wave has traveled across the room. At low enough frequency it has time to travel back and forth being reflected and canceling itself before we even hear it. 

Time delays in other words are irrelevant.

10" is not lame, you just need more of them. https://systems.audiogon.com/systems/8367 

The thing with subs, placement with the first one is time consuming and ultimately impossible. Because being only one, then no matter where it goes you get great big peaks and dips. The time consuming part is moving it all over the place before finally giving up and living with huge compromise, telling yourself it is really good anyway. 

Second sub placement is a bit easier. Now with 2 subs each one puts out less volume so the peaks are smaller and so are the dips. All you really have to do is put the second one somewhere a different distance from a corner than the first one. This will make the peaks and dips as different as possible from the first and give a more smooth bass response.  

This is where most of the improvement comes from, the smoothness. That is why it matters much less how good a sub you use. It is much more important to use a lot of them. With each additional sub the bass becomes even smoother, faster, cleaner, deeper and more powerful. Each additional sub lets you turn down the volume on the others. So you also wind up with a lot more dynamic headroom. Plus placement gets easier and easier. With four you can pretty much put them one to a corner different distances and be done. That easy.