Mushroom is blocking at Vale Guardian
I’ve tested an assortment of speed boost mushrooms. I’m fairly sure that you can get obstructed if you and your target are lined up just right. I think the obstructing spot is near the middle of it, though it might be slightly off center (it seems to include the center). You can usually see over it on angular terrain when you have the high ground. I also found it much easier for me to be obstructed using Thief’s pistols than with shortbow.
Some angles vs. the mushroom seem to be easier to get obstructed than others. I lured a tiger around various angles and could hit it fairly consistently at one angle, then I lured it 90 degrees to the right and was getting obstructed fairly consistently.
Most of the speed boost mushrooms, I had to go out of my way to get obstructed. However, some of them were a lot easier than others just given the flatness of the terrain, along with potential competing obstructions (eg. tall grass, not sure if that can obstruct, I could walk through it), as well as the relative locations of available enemies for me to lure.
I didn’t test it in the raid since I wouldn’t have been able to reach VG solo. Those mushrooms would be really great for testing since there wouldn’t be any other terrain that might invalidate the test.
I’m fairly sure that this issue is real, though I guess it is possible that my imperfect testing conditions may have yielded some false positives.