CAM belt replacement

I am changing cam belt on my vehicle listed above. I carried out the following steps:

1. Removed plugs to ease turning engine over and inserted a dial test indicator in number 1 cylinder.
2. Rotated engine to TDC on the dial.
3. Removed camshaft bearing cap nos 3 on both inlet and exhaust camshafts
4. Installed cam locks in place of bearing caps to lock camshafts in their timed positions
5. Loosened cam belt tensioner and removed cam belt tensioner and idler.
6. Using a counter holding tool to prevent stress to the camshaft components the 4 ribe bolts on the inlet sprocket were loosened and the 18mm bolt on the exhaust sprocket was too.
7. The new tensioner was lightly installed and the idler firmly torqued up
8. TDC on the crank was checked by finely moving the crank sprocket a couple of degrees to ensure number 1 was still at that position.
9. The new belt was placed over the crank sprocket which was then locked in place using a 19mm socket on an extension clamped to the hub
10. The belt was carefully installed and both cam sprockets were loosened and pushed to the right for this procedure
11. Maximum tension was then applied to the belt using the special t shaped tensioning tool and the lock nut torqued to 25Nm.
12. Both cam sprockets were then torqued up
13. Cam locks were removed and engine rotated twice back to tdc and both cam locks were reapplied to endure they fitted.
14. Tensioner nut was slackened and adjusted so pointer was aimed st center of hole this was extremely difficult to achieve the pointer was either aiming too high or too low but eventually it was centered at the hole and the nut re-torqued.
15. Engine then twice rotated again to TDC to check cam locks and tension but now the tensioner pointer had dropped below the hole indicating belt tension was too low.
16. Despite innumerable and careful attempts I have found it impossible to maintain the tension on the belt as indicated by the pointer on the tensioner which ought to be directed towards the center of the hole at TDC.
17. I was able to start and run the engine but the pointer was oscillating well above the hole ie about 8mm at idle there was also a chirp that went on revving up so I stopped the engine took rocket cover off and checked tensioner pointer at TDC now the pointer was well below the hole but before engine was started it was in correct position.
18. I have redone the job using another cam belt kit again the big issue is that I can’t get the pointer on the tensioner to point at the center of the hole at TDC or rather for it to return to that position when the engine is taken to TDC again.
19. Now I’m finding that when I try and get TDC on the DTI gauge the gauge is giving me different positions for this which is a another problem I don’t know if the gauge is sticking but it doesn’t appear to be on inspection and not can I see any carbon pieces down cylinder number 1 that might be causing the error.
20. I am at a loss as to how to complete the job unless I can tension the belt accurately and would be grateful for your advice.