Thank you very much. Now that I think about it, it is trivial. But I was not able to get before. Your answer clears a doubt. Thanks.
However, here is a curious question, as sum reduction will produce a larger gradient and thus the converging can be faster, why the choice of mean by default? We can always reduce the learning rate in order to regularize the steps if they are too big and we are running into not finding the minima. What is your take on this? Will be curious to know.
Have a good day and thanks again.
Best