LP Win:Loss ratio in Ranked

Within the last few months I have been only getting around 15lp for a win and sometimes even losing 30 for a loss... I don’t understand why this is the case... can anyone explain it to me? Here’s an example of my last game just now:

http://i.imgur.com/J5w2Wn6.jpg

Hopefully someone can explain this phenomenon to me... Because I don't feel like I'm doing particularly badly... And it's only when I play support that I get such a low ratio... when I play any other role I tend to get more, but I much prefer support and would like to try to resolve this without switching mains if possible...

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