> The guideline was to always use the imperative form if you knew there was a better way, especially if there's a precedent or it's a written rule in a guideline, but even for opinionated things.

Same here. We used imperative form too and never had any problems. All developers were matured enough to not take comments about technical stuff personally. I think as long as we are being direct and polite in the reviews, there should be no issues.