Xenon and I have a difference of opinion on Noise and Hosts. You can read more about our different points of view
here... I won't derail this thread by repeating them here.
But with regards to my POV, I'd give you my answer to your more specific example.
I’m really not trying to be dense, let me try a more specific example. Hacker Jack is sitting in his van 100 km from the run site. This gives him a 5 noise rating. Fortunately he has a rating 6 cyber jack and cyberdeck. He can just barely affect the target with a -5. Due to that, or just bad luck he alerts the security spider. The company is on a budget, so the spider has a rating 4 deck and jack. The physical distance between them is still 100 km, so can the spider even affect Jack? Presumably he can defend against Jack’s attack, but the noise should prevent him from targeting Jack, right?
Ok, Hacker Jack is 100km away from the facility the run will infiltrate, resulting in 5 Noise, and no other local conditions inflict more Noise on him. So he's able to hack icons networked to the Host at -5 dice (or even a smaller penalty, if he's got Signal Scrubber or other Noise reduction tricks in play). Now, Hosts have a lot of similarities to PANs but they're not the exact same thing as PANs. For example, you "Enter" Hosts (see pg. 181) but when it comes to hacking PANs, you just achieve whatever level of access you desire and go from there.
Now, it doesn't SAY you ignore distance after executing the Enter Host action, but IMO that's a simple oversight and the intent is that you do cease to count distance based Noise after entering the Host. But presuming you do ignore the distance based Noise- then the IC and Spiders have no Noise-based trouble taking actions against a Persona inside their own Host.
Of course if you DON'T presume you ignore distance when inside Hosts, then yes on top of the problem of "how does global commerce even work" you have the problem of potentially having Spiders and IC being unable to affect a hacker, which surely isn't the intent.