I am not sure what the formula for getting valour is, but I find it silly that your chances of valour depend not only on the performance of your team, but also on the performance on the other team. I will provide some examples to illustrate my point.
Example 1:
It is a horribly unbalanced round of battle with the enemy team barely only a handful of players while ganking your team. Most of your team didn't even reach 10 points in the round, but you managed to hold out fairly well and got 30 points, making you have a way above average score. The valorous top gankers on the other team got 40 or even 50 points with most of their team having a good 20 points due to proximity score. Which makes the top gankers on their team receive valour instead of you. There is no doubt in that the top scores of the other team did well, but you can't really compare the circumstances in which they got 40-50 points and you got 30. Considering the circumstances I'd say you were as valorous if not more than they were.
Example 2:
Oh Siege, valour on Siege, ain't that something. You are playing a shitty ladder map and are attacking. You charge up the ladder valiantly again and again and you manage to do incredibly well. Accruing 120 points in the round. You are well on top of your team and even though you didn't manage to win no one can say you didn't try. Then looking at the other side of the scoreboard, 4 people with over 200 points. All of them high damage 2h who spent their round camping the top of a ladder, with loads of proximity points being awarded to a lot of people. Of course they were very useful for their team, but you can't really compare the circumstances in which they got so much more points than you.
My suggestion being that valour should only depend on the scores of your team, because they got those scores in comparable circumstances. This goes especially for siege, where as an attacker you often have no chance at all to gain valour. It goes for battle as well though, being on a winning team makes getting points a lot easier. Comparing apples and oranges makes the valour system unfair. I don't know why the system works like that in the first place, but it is not too late to change it.