When more than one side booster is added to a first stage to increase thrust and they are distributed uniformly around the core (as opposed to those shown in links below) thrust does not seem to need to be angled. They could all point straight down (except for dynamic thrust vectoring for steering) due to symmetry.
- Why do the shapes of these two exhaust plumes from an Atlas V 411 look different?
- How does Atlas V maintain stable flight with asymmetric solid rocket boosters?
In the two images below, both from the recent NASA Spaceflight article Beidou-3 MEO-5 and MEO-6 launched by Long March 3B it looks to me like the exhaust from the boosters is angled outwards, I've added an annotated, cropped, and enlarged version to better show what I think that I'm seeing.
Is this in fact the case for this launch, and does this happen frequently?
![Beidou-3 MEO-5 MEO-6 Long March 3B]https://i.stack.imgur.com/vJJZQ.jpg