The positioning and circulation of your cooker should not be an issue. If you wish to check it at all, run the unit in the container without anything in it to cook and add a couple of drops of dark/strong food colouring the the water bath at the opposite end. Observe how quickly and thoroughly it mixes in with the rest of the bath. Do this with the APC on it’s initial bath warming and again when the bath is up to temperature. Anywhere that the colour hasn’t reached is likely to be a cold spot. In your case it will be useful if you can observe from the side as well as above.
I would also suggest getting a thermometer and checking the temperature at the base of the bath. I don’t know what material the vessel is, but you could try a surface reading from the outside of it at both the bottom and top of the container at the opposite position to the cooker. This will give a fair indication of how well the Anova is stirring the heat to the bottom of the container. Of course, this won’t work if you’re using an insulated container.
A note about Heston’s eggs. They are a very lose scramble, even when they are right. It’s also worth noting that egg sizes vary greatly. It’s extremely possible that the eggs you used were considerably smaller than those used for the recipe. This would cause a lower egg to dairy ratio and also impact the set.