Option 02 · Fails run-off
The trainer clearances are fine here. The treadmill is what rules it out.
Dashed outline = minimum clearance envelope, 24" each side and 36" in front · shaded = working zones · stair wall at left
Turning the treadmill puts its 83" deck across the room's short axis. The room is 123" wide, so whatever the deck does not use becomes run-off: 123 minus 83 leaves 40". That figure is fixed. Sliding the machine along the back wall moves the deck but not the sum, so no position on that wall produces a compliant run-off.
ProForm's own manuals specify at least 8 ft, 96", of clearance behind the treadmill and 2 ft on each side. ASTM F2115-05 sets a lower bar at 39" behind and 20" each side. Where a manufacturer and the standard disagree, the accepted practice is to follow the greater distance, so 96" governs here. At 40" this option misses either figure by a wide margin.
It is travel time, not padding. At 6 mph a runner covers roughly 106 inches per second, so 96" is about nine-tenths of a second of movement. At 10 mph it is closer to half a second. That is the window between losing your footing and hitting whatever is behind you.
If your ProForm folds, this is an excellent parked position: compact, out of the traffic path, and it leaves the room wide open. You would pull it out and pivot it back to the long axis to run.