My team was going through inspection and the ref told us that since the corner of where our wing was attached to the robot was concave. But I was also told wings can be concave and legal.
Wings can be concave and legal but have a high chance of causing multiple triballs possession.
Better to read the game manual yourself, verify what someone tells you, and know exactly what the rules are: VRC Over Under Game Manual - VEX Robotics VRC Over Under Game Manual - VEX Robotics
Use the search function and look for concave
As you read the Game manual, note that it will never tell you if a particular mechanism or strategy is legal or illegal, but rather what makes something legal or illegal is how you use the mechanism or apply a strategy.
https://www.robotevents.com/VRC/2023-2024/QA/1610
Concave spaces are ok possessing more than 1 tri-ball is a violation. At inspection they may warn you of a concave structure on your bot that could potentially possess more than 1 tri-ball. Make sure you read and understand the difference between plowing and possession. Then make sure you don’t possess more than 1 during the match.
In Q and A it was said as a gray area but repeated after it being determined illegal could lead to a DQ