Regardless, the iPhone SE did not sell _as_ well in Japan due to a variety of factors, not the least of which being that the iPhone 7 introduced built-in Suica support.

Suica is a mobile cash card technology used at stations for transit, convenience stores and restaurants for purchasing, and vending machines -- among others. Given the lack of support by many credit cards for Apply Pay in Japan (for example, you cannot add a Visa card to your iPhone due to JP-specific Visa restrictions), it's no surprise that this was a major selling point of newer models.

In my opinion, manufacturers have not provided a high-end, small form factor device to sufficiently test the markets. Without doing so, it's too easy for people to make the claim that people have already voted with their wallets for larger phones. I sincerely hope the rumors of a 5.4" iPhone 12 are true (as it should be somewhere between iPhone 5 and 6 form factors, from what I gather).