Even pushing the cans closer to your ears is going to affect the way they sound. Depending on the headphone, it may have different effects. FR is measurable on headphones, but from my understanding, it's particularly hard to gauge what an objective graph really means. I have also heard from...

Frequency response graphs and most measurements can be extremely misleading. Also, a flat good Fr that you would expect to see on a good speaker is not necessarily what a good Fr for headphones will look like at all. Best thing to do is start compiling a bunch of tracks that you have your ear...