Keyed mortise and tenon

The next project has keyed mortise and tenons, but before I ruin perfectly nice cherry pieces, I thought i should work out a few kinks. Here are the first few attempts. I'm trying to get a very slight 5 degree angle to the entry point, as the receiving mortise is a panel type leg for a bench, and has a slight tilt. I have already learned if you over tighten the key you will take a beautiful chunk out of the remaining mortise... So gentle taps only!