Give more IP/XP for shorter game length instead of longer

It seems like the longer a game goes, the more IP/XP is given typically, but I think it should be the opposite. For instance I just went 10/1/16 with second highest cs, and only got 80's IP and XP even though I took a number of towers, helped with dragon etc... all because the game was only 27 minutes long. Had the game gone longer I would have gotten a lot more, even if I were playing badly, purely based on the game length, so I think players should be rewarded the faster they're able to finish a game, due to a good performance.