Question How are observations padded when using more than provided?

I am doing research into multi agent reinforcement learning, and need to provide a large number of observations, as I am adding observations for other agents the more agents are in an environment.

i.e. if there is one agent it has 9 observations, but if there is two in one environment, it will have 13, three will have 17 etc.

Meaning I need to supply a larger amount of observations, so when I initialise the brain from a previous run, it has enough observations.

So Unity raises the warning "observatoins will be padded", but how are they padded? I can't seem to find any documentation on it and want to write about it in my report, any help would be greatly appreciated, and happy to supply additional information if needed.