Hello Patrycy Przybysławski,
Answering your question, if you are developing a design for 375*667 (iPhone 6, 6s, 7, 8 ), you should keep in mind that it will be rendered at 2x. So you keep 22x22 icon in your design. But at the export stage, you should select @2, and you shouldn’t ‘reserve’ anything.
It’s great that you are starting to learn the differences between iOS and Android. It will make your design process easier and qualitative. We are glad that our article was useful to you ;)
Thank you for sharing your thoughts with us!
Your statement makes sense, however, we don’t fully share your opinion meaning that “up front design” is not fit for complex applications. It may not be used because it may take up more time and funds, but this approach will help avoid bigger problems down the road.