From what I've seen of the EPP FPV, it's a great plane but because EPP is so draggy, the max endurance is stuck at around 30-40 minutes, no matter what mAh you're carrying. I've also seen the comments that Arman refers to, and perhaps there is something to it - it's an in-house designed plane, and there's always variable quality between individual planes designed internally by HK.
@Carbon, did you weigh the fully loaded plane? In my head I'm thinking that 2x2200s and a gopro is about 500g plus a fair bit of drag from the GoPro. Also, any difference with the flaps down?