The weighting is basically a way of saying how likely each scene is relative to other scenes, since they're chosen randomly. For example, a scene with a weight of 6 is 6x more likely to be chosen than a scene of weight 1, 3x more likely than a scene of weight 2, and half as likely as a scene of weight 12.
For the rimming scene specifically, the highest chance you can get for that scene is 1 in 3 (with equal chances for the anal and oral scenes), with the following conditions:
- Steele must have a penis and have performed oral on her before in order for the scene to be available at all. So if your Steele doesn't have a cock, that would explain why you've never managed to get that scene before.
- Steele must not be in heat or rut, since those scenes are much more likely to be chosen (6x for the heat scene, 3x for the rut scene). Those scenes also have a 48 in-game hour "cooldown", so you can get away with being in heat/rut if you've done the scene(s) in the past 48 hours.
- Finally, Steele's smallest penis must be > 6 inches long; otherwise, the small penis humiliation scene is available at the same weighting, reducing the chance to 1 in 4 (since there's now four scenes of equal weight to choose from rather than three).