If this is your only sub, then you are going backwards. :)
Put the sub in your listening location, and measure the bass at your possible locations. When you find the location with the smoothest bass, that's where you want to put your sub.
If this is your first sub and you are placing a second, then your approach is correct.
Also, remember that bass traps and EQ help fix what placement cannot. I wrote about this more here:
https://speakermakersjourney.blogspot.com/2020/04/how-to-not-buy-subwoofer.html
Put the sub in your listening location, and measure the bass at your possible locations. When you find the location with the smoothest bass, that's where you want to put your sub.
If this is your first sub and you are placing a second, then your approach is correct.
Also, remember that bass traps and EQ help fix what placement cannot. I wrote about this more here:
https://speakermakersjourney.blogspot.com/2020/04/how-to-not-buy-subwoofer.html