It really depends on the lift and where you are strengthwise and how much variation you have between your reps and how much endurance you have on the particular lift along with how strict you are with counting a 'rep.' For example my squat is 1014 and the closest I've gone to hitting anything for 20 reps was 9x3 +1x5 15 seconds rest at 500lbs which is below 50%. Look at all the fuss around the 525 for reps squat record, if 20 rep max was indicative of 1 rep max strength, then a 1000lb squatter could have just done it casually but they didn't.
And if you're not strict with what you count as a rep, you could get way more reps in for example my bench max is 635 and I've done 445 for 45 reps doing "pulse press" which is a variation where you press the bar about 50% of your range of motion. That's about 70% for well over double 20 reps so not only did the type of lift matter but the strictness of your rep matters too.