If we approximate an MLP layer with a bilinear layer, then the effect of residual stream features on the MLP output can be expressed as a second order polynomial over the feature coefficients $f_i$. This will contain, for each feature, an $f_i^2 v_i+ f_i w_i$ term, which is "baked into" the residual stream after the MLP acts. Just looking at the linear term, this could be the source of Anthropic's observations of features growing, shrinking, and rotating in their original crosscoder paper. https://transformer-circuits.pub/2024/crosscoders/index.html