“… The biggest upset in the 3rd Round: Kidderminster 2-1 Reading. 6th-division side Kidderminster Harriers (of Worcestershire) defeated 2nd division side Reading. At kick-off, Kidderminster were 5th in the National League North [#120 in the League pyramid; although normally that would be #121, but there are only 23, and not 24, teams in the 5th division this season]. Reading were in 21st place in the EFL Championship [#41 in the League pyramid]. So the difference between Kidderminster and Reading was 4 League-levels and 79 league-places. …”
billsportsmaps
2021-22 FA Cup, 4th Round: Location-map, with fixtures list & current home league attendances
FA Cup
BBC FA Cup