I would say the 11.5 oz. weight is the main problem[X(]. Also, if you're using a HS-55 for pitch servo it's not up to the task of
holding pitch under loads you'll see at that weight. I have a Yak that weighs about 8 oz. but it has the Ikarus unit with the less
powerful S2 motor. Personally I think the 2208/34 is too low Kv to provide a lot of thrust with those blades. I feel your pain though
if that helps. I've spent a bunch on this whole VPP/EVP thing and haven't had good results yet[]

Steve