No.
We're talking about valour here, not something that every 1/4th of the loosing team gets "everytime".
Also, based on my own experiences :
-valour has nothing to do with kills
-valour has something to do with proximity with a bunch of ennemies
-valour may have something to do with life lost, while still alive, for a long time
-valour, thus, has something to do with how long you remain alive
I think it's :
-based on the longer time ennemies surround you while you're not in full health.
Scenarios:
You hide during the all round, are the last of your team, get couched by a cav : no valour
You fight while flanking, kill one guy, loose a bit of hp, then flank the big force wich is slaughtering your allies, survive a bit in the clusterfuck. The last guy die in less than 1min after you die : valour.
You're a roofcamper xbow with a side weapon. You shoot people down. You get shoot but survive. You're the last on the unreachable roof, ennemies are surrounding you. You jump down without getting damage, kill a wounded peasant you had noticed before, block a few times while getting ganked, then finally die : valour.
The problem with this system, is, you may have noticed, the third scenario. Only give valour to players having no horses and no ranged weapon, and it'll become a bit more glorious "valour" than now.
Problem with your suggestion, has dangah said, is that very good players will have a permanent x5. And yes, that's bad. Nothing more frustrating for a new player, to get "balanced" in the loosing team, while knowing that the best player of their team doesn't care about the result since he always get valour. I wouldn't mind actually if the "valour" was more restricted : you can't get it twice in a row, for example.