With this type of joint, usually called a skarf joint which is used a lot in boatbuilding, 45 degrees is almost never used, not enough glue line. You want the angle that is most parallel to length of the board, within reason but at least 4 to 1. So, for 3/4"x 3/4" material the joint would be at least 3" long but more likely 4" to 5". For a 2" wide board I would go for 6", and so forth.
An easy way to make this perfectly in these smaller sizes is to use a chop saw. First, set the saw at 90 degrees, clamp and cut something to use as a guide. then rotate the blade to the correct angle which will be somewhere near 20 degrees. Put both sticks, clamped together, on the saw table against the 90 degree board you clamped and cut first such that the sticks are projecting straight out from the saw, and cut both at the same time.
For wider boards I would use a portable saw and a guide, but the principle is the same, cut both at the same time with the boards side-by-side. Then, no matter what the angle is, they will match.
There is no reduction in width at all.
Last edited by Brian(J); 11-07-2016 at 11:53 AM.