Most of dad's attacks were below 20,000'. On the raid to Pforzheim he bombed at 8,500'. Most bombed at less than 9,000'.
I'm presently going through the ORBs for 433 Squadron for 1944 working on a little (actually large) project. The lowest reported altitude so far was 2,500 feet on the evening of June 6/7. Here is what is reported as the bombing altitudes for the missions in January through March, 1944:
Jan. 20/21 vs. Berlin = 20,000 to 21,700
Jan. 21/22 vs. Magdeburg = 20,000 to 22,500
Jan. 28/29 vs. Berlin = 20,000 to 22,500
Jan. 30/31 vs. Berlin = 20,000 to 21,000
Feb. 16/17 vs. Berlin = 20,000 to 23,500
Feb. 19/20 vs. Leipzig = 21,000 to 25,000 (I suspect the latter is a typo)
Feb. 20/21 vs. Stuttgart = 21,000 to 23,000
Feb. 24/25 vs. Schweinfurt = 21,000 to 23,400
Feb. 25/26 vs. Augsburg = 21,500 to 22,000
Mar. 6/7 vs. Trappes = 13,000 to 13,600
Mar. 7/8 vs. Le Mans = 13,000
Mar. 13/14 vs. Le Mans = 11,500 to 12,000
Mar. 15/16 vs. Stuttgart = 20,000 to 23,500
Mar. 18/19 vs. Frankfurt = 20,000 to 22,100
Mar. 24/25 vs. Berlin = 19,500 to 22,000
Mar 26/27 vs. Essen = 19,300 to 22,000
Mar. 30/31 vs. Nuremberg = 21,000 to 22,000
Bombing heights depended in part on the town's defences.
Yes, that was certainly a part of the consideration as well..