Properly, this piece should be called a “raised rafter tie” if its primary mission in life is to resist the lateral thrust imposed on the top of the walls due to the absence of a structural ridge, queen post purlins and ties, braced purlins, etc.

When it is placed more than 1/3 of the height of the ridge distance measured off the plate, it imparts such signicant bending stresses in the rafters, they usually have to be up-sized to compensate. Nevertheless, if one is willing to make the necessary compromises, it can be used as a “raised tie” to prevent the spread of the walls due to the thrust. Also, this is a very popular configuration for heavy timber trusses.

Once the rafter component is properly sized, the critical design requirement is the strength of the connection between the tie and the rafter component due to the significant tension in the tie.

Hope that’s helpful. I’m probably “preaching to the choir” here, but I really don’t think “collar tie” is the appropriate name.

And, if you’re using a collar tie to resist wind load, I think it’s simpler to just put a piece of coil strap across the ridge or a few toe nails from the top of the rafter into a ridge board usually do the job as well. Both or much more economical than a collar tie unless you have an exposed ceiling which you wish to flatten.

Thanks for listening (reading).

David