Wondering what the difference is between something being "obvious" and "blatantly obvious"...
If I'm on the bases, I tell my partner to feel free to come to me on a checked swing no matter where I'm set up.
"But! But! But! You can't see that from there..."
Maybe I can, maybe I can't. If I can't, then I'm not going to overrule you and call a strike. But if I can, I will.
It's not "impossible" to make this call from sub-optimal positions. Just don't guess at a call. If you really can't tell, the default is "no swing". You did your job as best you could- be happy with that and move on!