Only horsewear for decades now. Never had this happen. They have never blown over, the horses have never caught up in them (despite having two ‘super rollers’ that roll every day, all around, both sides). This includes fly sheets in the summer (30C + , hot and muggy) and thick winter blankets & liners in the winter (think -20C and tundra).
Having had to deal with some none horsewear blankets with annoying as heck features (neck loops you can barely fit straps through, requiring you to duck under the horses chin to try to fasten; snaps that are too small and fiddly to maneuver with gloves on etc.); I’m team Horsewear all the way.
Your mileage may vary, of course … but may I kindly suggest that some issues may be resolved by proper fit? The seam for the tail flap should end just past (maybe an inch or two) past the dock of the tail. Too large and you’re going to have shifting.