It's not explicitly mentioned in this way here, but I feel like the underlying assumption is something like "If you think they need the $20k plan, and you sell them on $10k, they'll increase to $20k based on usage then expand into $30k [(this is basically the chart in the article)] - but if you sell them on $20k, they'll stay there."
I don't see why you would intentionally undersell. How does that have any bearing on whether or not they expand into higher tiers, or whether or not they refer new customers to you?