MBP runs slower in bootcamp without dual screen?

[Wafflausages]

At home when im gaming on League of legends w/ an external monitor i get about 50-70fps then when im on the go (plugged in and the power setting is still on high performance) i get about 30-40 fps why?

 

[Detrius]

It's possible that Windows can't switch between multiple graphics chips like Mac OS X can and that therefore you're stuck on the integrated graphics for the built-in display.

Just a theory.