Sorry, was this confirmed by the DEVS?

I understand the question and I have pondered this one myself.

1) You start the game with 50%.
2) So you have home bonus and you watch the match and the other manager is not watching = +13%

The question is this:

1) Do you get +13% of the 50% = ~56%, or
2) Do you get +13% to add to the 50% = 63%

This may seem simple to most but we start working in percentages so it seems logical to work either way.

And sometimes you see possession greater than 70% even with no spectators and hardly any bonus possession, so we know formations, quality and tactics have effect on possession.

We can also surmise that some formations will grant more possession against certain formations. We know the NGE takes this into account and will will most likely NEVER know the real numbers, but through testing we should be able to approximate the numbers. This would take a ****load of time and testing and would not really be worth it if the NGE is tweaked every season.