I have a phantom 3 4K which I have owned for a couple of weeks. Whenever I go over 25 m high I seem to get the weak video transmission despite the fact that the controller signal shows full. It's really frustrating. I thought I would be able to do a few hundred metres without issue. I am running the latest firmware and all on an iPhone 6plus. Any ideas? Relinked the controller already and calibrated it but no better. Is it safe to still fly even though I can't see the image and just use gps to carry on? I am under the impression if it totally loses signal it will return home?