[@KatherinWinter]

Argus is pretty much just improvising in an attempt to prevent Richard and Amaya from getting themselves killed and salvage this trainwreck of an operation. He doesn't know for sure if her powers have that much range, so he's taking a gamble and hoping for the best.

The exact size of the tunnel has also never really been properly defined, so I was going off of best guesses and the time I went on an underground city tour in Seattle where we went through some of the older sewers.