Multicopter PID Tuning Guide Rate Controller

Hi Folks,
I am part of a team that working on a prototype for a heavy lift drone. I am using the Holybro Pixhawk 4 FC and I am having trouble trying to fly the prototype. I am thinking that problem is in the air frame mixer, I am using the generic 500 mm X quad air frame, the prototype is 14 in diameter. Big difference, so I am thinking that I need to reduce the Gains in the rate controller a lot and start over bringing them up very slowly. I have done all of things that the article talks about on getting ready to tune the drone.
Any thought would be great.

Mike

Hi Folks,
I just noticed that editing on the last post is not that great! Hi! The Prototype Drone is 14 feet in diameter, not 14 inches real big difference!
One of the team members is sick so I have not had a chance to try out my ideas yet.
Thanks Mike