How to get bolts tightened correctly without a torque wrench

I've looked around the internet for a comparison chart that compares torque angle to torque wrench value settings for tightening fasteners.

Currently, I've examined only M6x1.0 and M6x1.25 fasteners, While I've found that I've been tightening the M6 fasteners correctly, I have evidently always overtightened the M8 ones.

I used a torque wrench on a nut clamped into my bench vise to torque each fastener to the recommended tightness using a torque angle wrench to measure the degree or radian movement.

To achieve the recommended torque of 80-90 inch pounds, the wrench needs to be turned 80 degrees.

For the M8 bolt, to my amazement, 18 ft. lbs. needs only a 30 degrees turn, before the wrench clicks.

All these years, I've been over tightening 8mm bolts, although I usually do no more than a 45 degrees turn.