I would be very careful of putting a 20+mm in the 2013 Accords . While they are using a similar rear suspension , the front is struts now with 10mm smaller front bar than 8th gen . that is huge change . I guessing they have firmer struts compared to the older setup due to being struts now . spring rates it probably higher with this setup .
Make sure for ones using this you test it out "good" to make sure oversteering will not be problem in wet/dry, when throttle lift on turns etc .
Oversteering is worse than under when it goes to far . Good thing the VSA will try and kick it but you don't want that happening if at all possible .
Looking at specs I would think the 17mm tsx would be good match with front .
I had the same concerns before doing this modification, but for the price I had to try it knowing that I could always reverse the modification or go with a thinner bar.
Also, I did extensive research on the 8th generation forum where this modification is popular as well as other Accord forums. Other owners do not have any oversteer, or snap oversteer problems even when going with the even thicker 24mm Progress rear sway bar. I understand that they have a thicker bar up front from the factory to equalize with the rear, but continued based on knowledge about other vehicles with similar suspension setups and aftermarket rear sway bars.
While your concerns are valid, I do not believe this to be an issue as I have over 3,000 miles on this modification and do not feel any adverse effects thus far.
I have pushed the car hard through corners and have tried to purposefully make the car snap oversteer by throwing the weight around on and off the throttle hard. I put the car in situations that I normally would not do. I could only get the VSA to come on a few times. The car pushes through corners and just rotates much better. You can feel the oversteer coming on slowly as you push harder.
Many 8th gen owners went with the 17mm bar initially and felt some difference, but many wished they had gone with the 20mm bar in the end once people started finding out that it fit. And now Progress Technology has a 22mm and 24mm rear sway bar available. The only concern so far is that the rear sway bar mounts are not very beefy from the factory and some owners with the larger bars have broken said mounts. Also, the end links may start to fail when used with the larger bars. Aftermarket solid spherical end links are available from Progress Technology.
I'm currently searching for a front bar that will fit to balance out the car even better. A common upgrade for 8th gen owners was the TL AWD front bar, but our front suspension being different now requires different solutions.