The dreaded droop…..

[MikeD55]

Any suggestions on how to combat this?

[Gulf]

It begins in the planning stage, studying some of the builds that covered the terms of "proper "arch placement" fore and aft. Once that is determined, study some of the builds that have the terms "dreaded droop".

[mongota]

Any suggestions on how to combat this?

Start with the correct placement of the arch within the dome as Gulf mentioned.

When building the arch, cut your arch bricks so they coordinate with the geometry of the dome. See my link below, which is just one method. When setting the bricks, use an IT to set your bricks and don't use longer bricks when transitioning from dome-to-arch, across the arch, and then transitioning back arch-to-dome. Stay with the half- or third-sized bricks that make up the rest of the ring you are working on.

There are a lot of examples of cutting the arch bricks, find one that makes sense to you. Here's a link to a page where I described how I did mine. I had a difficult time envisioning this during the planning of the build, but once it was all in front of me, it made sense:
https://community.fornobravo.com/forum/pizza-oven-design-and-installation/pompeii-oven-construction/18881-mongo-s-42-ct-build?p=392414#post392414

[JRPizza]

You are smart to ask! As I said in my thread - "avoid the droop" is not really advice! I tried to explain in the post below how I got my droop and I think if I built again I could prevent it from happening.

https://community.fornobravo.com/forum/pizza-oven-design-and-installation/pompeii-oven-construction/380308-39-inch-corner-build?p=381405#post381405