A much less famous, perhaps unknown, triangle can be a helpful image. The boast triangle.
The boast triangle has the ball as the apex and a portion of a sidewall as the base. One leg of the triangle is the line connecting the ball to front corner. The other leg is the line connecting the ball to sweet spot on side wall. The base is not the entire sidewall but just the portion from the front corner to the sweet spot. The front corner will not move. However, as the ball position changes, the apex moves as does the sweet spot.
(Figure 613a)
The striking point “2” has been used in other figures.
The sweet spot is marked on the side wall. Any boast deeper than that is deemed not good. Any boast between sweet spot and the right front corner is deemed good. Opponents must not block any chosen boast to this portion of the side wall. Inside the triangle is a no go zone.
If the striking point is changed, the triangle will change.
(Figure 613b)
The striking point “6” has been used in other figures.
A striking point that close to the front wall leaves most of the court open for the opponents to be safe. However, interference in this case would be egregious.
(Figure 613c)
Ah, there are two boast triangles for every striking point. One triangle for the near side wall and another for the far side wall. In most cases the right wall opponent must vacate the boast triangle on the right wall and the left wall opponent must vacate the left wall boast triangle.
Rule 5 doesn’t make that distinction. Both opponents must be clear of both boast triangles.
Rule 5 is clear, as a defensive player, do not go into a no go zone. Motorists must not exceed the speed limit, but they do. If they are caught there are consequences. Squash is different from most sports and certainly different from speeding violations. A doubles referee has the duty to stop play for some infractions such as the ball going out of play. However, flight interference violations are not called by the referee. It is up to the striking player to stop play and ask the referee to make a judgement; request a let.
If the referee judges that there was interference, then either a let is granted, or a point is awarded. For flight interference the referee assesses the readiness of the striker. Was the striker in position to strike the ball and was the let requested the instant before the ball would have been struck? When an opponent is judged guilty, the situation will influence whether a let or point is awarded.