Try this; 1. every PR review call out one neat thing you _really like_ and maybe ask how they figured that out
2. Be explicit in the dichotomy between "recommendations/nits" and "you shouldn't merge this". Weight things toward the former. Have a style guide for the latter things and be very conscious of when someone is violating the actual style guide or just your own biases. If you really have high "standards" write them down... Otherwise they are just whims, not really standards.
To put a finger point on the advice above: you should _never_ be enforcing "your standards" but the "team's standards". If you can't tell the difference, that's its own kind of problem.
