Creating polynomial contrast for parameters

Sorry, your question fell through. I can’t comment much on hypothesis as I don’t really use Bayes factors. Overall, I find it much easier to evaluate models using their predictions - I’ve written about this in a different context here: Multivariate model interpreting residual correlation and group correlation - feel free to ask for clarifications (this lets you for example test directly whether your predictions are within some ROPE).

Does that help at least a bit?