Matching the challenge to your skill and running a fixed pre-performance routine have real, consistent support for producing focus. Attention and mindfulness training in athletes reliably raises flow and lowers competitive anxiety. The calmer-and-more-focused effects are stronger and steadier than the raw performance numbers, which vary study to study.
The four percent rule for setting a challenge just past your skill is a coaching heuristic, not a lab constant. Treat it as a feel, not a measurement.
Quiet eye, the longer final gaze before you move, is promising and still argued about. Run it as an experiment on yourself and keep it only if your own logs vote for it.
The deepest version of the state cannot be summoned. Senna drove a lap in 1988 he could not explain afterward, and it frightened him enough to slow down. This app builds the conditions and raises the odds. It does not hand you the state, and anything that promises the state on command is lying.