A fixture used to produce an angle had better by right on, as on the Donkey Ear for the Vogt Shooting Board. Close ain’t cuttin’ it. It’s easy to get in the ballpark but not to hit home runs consistently.
If you want to bevel a plywood edge to 45° the tablesaw is the obvious choice.
I have found that, no matter how carefully I set the blade angle, the results can be inconsistent. Material can be less than ideally flat, the reference edge against the fence not as straight as expected, and the angle a fraction of a degree one side of 45 or the other.
A technique I have developed that delivers the accuracy I want is to start with the tablesaw, then use a jointer plane to shoot a small, straight flat on the knife edge, and finally to joint the bevel on the router table using a large bit.
My router table fence can be set with an out-feed fence to remove about 1/32”. Notice in the photo that I have inlaid a strip of acetal in the MDF face of the out-feed fence where a very sharp edge would wear a groove in it.
When I set the bit height, the sharp edge lands in the small space below the bearing.
There is snipe for the first two inches of the piece to be beveled that I account for as waste. Tapering the leading edge helps to guide it onto the out-feed fence.
Scribble on the edge to be jointed lets you see if the job is completed when it is fully removed.