[Back In The Saddle]

There are two distinct cases, it from what I've read to this point it sounds as though the criteria for the two cases is being mixed together.

ART. 4 . . . When screening a stationary opponent from behind (outside the visual field), the screener must allow the opponent one normal step backward without contact.
ART. 5 . . . When screening a moving opponent, the screener must allow the opponent time and distance to avoid contact by stopping or changing direction. The speed of the player to be screened will determine where the screener may take his/her stationary position. The position will vary and may be one to two normal steps or strides from the opponent.

The OP used the term "blind screen" which isn't actually defined.

If you define "blind screen" as being restricted to 4-40-4 (i.e., a screen on a stationary opponent outside the visual field), then the notion of a stride has no bearing on the discussion. The standard is "one normal step backward". If the screened opponent steps backward and contacts the screen before the foot comes down it's a foul.

If you define "blind screen" to mean any screen the opponent doesn't see, then you also have to consider 4-40-5. You have to consider both screening stationary opponents as above as well as moving opponents where the screener must allow "time and distance to avoid contact" and judge that time and distance in steps or strides.

As for the difference between a step and a stride, a stride is a step taken while running.