I can't really answer the poll. You asked if ch and sh were similar.
- Yes, in terms of shape they are similar. They are more similar to each other than they are to the other shapes.
- Yes, in terms of what follows, they are similar (based on the numbers).
- No, they are not similar in terms of how often they fall at the beginnings of tokens, but is the difference enough to be statistically different?
- No, in terms of what precedes them, they are dissimilar (based on the numbers).