Dennis, I think that's expected, right? Two-way on its own can exploit nothing about individual characters - it only preprocesses the needle to break the possibility for quadratic-time behavior due to periods in the needle.

It sounds like you switched the current code's Sunday-ish approach to a more Boyer-Moore-ish approach. That probably hurt, and especially for shorter needles (where Sunday can yield a maximum shift of len(needle)+1, not len(needle) - the "+1" is more significant the smaller len(needle)).

Sunday gave 3 variants of his basic algorithm, and in his tests they were all faster than Boyer-Moore, and more so the shorter the needle.  Just FYI, here's a scanned PDF of his paper:

https://csclub.uwaterloo.ca/~pbarfuss/p132-sunday.pdf