The only thing it can be then is the followers are worn differently, not allowing clearance for the valve to be closed.
Take a look through this. It describes how to adjust valves. It shows how to mic thickness. I suspect when the followers were mixed up, it caused this issue. The attached pics correlate with the directions.
2006 Subaru Outback F4-2.5L DOHC Turbo
Vehicle Powertrain Management Tune-up and Engine Performance Checks Valve Clearance Adjustments
CAUTION: Adjustment of valve clearance should be performed while engine is cold.
1. Measure all valve clearances.
NOTE: Record each valve clearance after it has been measured.
2. Remove the camshaft.
3. Remove the valve lifter.
4. Measure the thickness of valve lifter with a micrometer.
5. Select a valve lifter of suitable thickness based on the measured valve clearance and valve lifter thickness, by referring to the following table.
6. Inspect all valves for clearance again at this stage. If the valve clearance is not correct, repeat the procedure over again from the first step.
7. After inspection, install the related parts in the reverse order of removal.
Let me know if that helps.
Images (Click to enlarge)
Tuesday, December 3rd, 2019 AT 5:31 PM