iOS design under 640px or 750px?

Question

iOS

We were given a task: to complete the design of screens for the application.
They gave out a concept for iP6 750px.
But I usually do under 640px and it seems to me that this is correct.
Because what can fit into 750px may not fit into 640px later.
I would like to know the opinion of others on this matter.

Answer 1

What is in 740 can be proportionally reduced to 640