increased power usage after upgrade from kinectic to lunar

Hi

I have just upgrade and power usage is double or more under lunar. Kernel version went from 5.19.0-43 to 6.2.0-20.

Running powertop, I see that C8 is being used with 5.19 but 6.2 does not go to a higher power saving state than C3.

I tried the Ubuntu kernel from jammy ie 5.15.0-73. It also uses C8.

I have also tried the 5.15.108 & 5.10.17 mainline kernels. Both of these do not go to higher power saving state than C3.

All these tests have been run on the same partition ie. only the kernel version has changed.

So it seems to me:
1) Ubuntu has applied a patch to the mainline kernel that improves power saving in 5.15 and 5.19
2) This patch either hasn't been applied to 6.2 or no longer works.

Can anyone suggest what I might try next?
or, give me a hint about where in the kernel code power saving is managed?
or, should I leave it to the experts and report a bug?

Thanks