If you want to push margins, larger devices selling for higher absolute prices are a better option.
Imho, it's harder to convince people a "smartphone" is worth USD $1k+. But a laptop / tablet replacement? That's reasonable(!) compared to a MBP...
Given Apple's build costs don't scale with device size (++screen, +battery, +gpu/mem), selling the same internals in bigger devices for more is a win.
So you continue expanding device size and price until you discover the market boundaries. And unlike Samsung S*/Note, Apple has the ability to say "These are the only form factors this generation, if you want the newest iPhone..."