Wrong laaa... retarding ignition timing is not to lower compression ratio...
to lower the compression ratio the VVTi or iVtec or variable valve technology will keep the intake valve open much longer than its required so the mixture will reverse back into the fuel injector chamber thus lowering the compression ratio

this also works with retarding ignition timing to compensate for the low RON or premature ignition (Engine knock)...

but if your engine is design for Lower RON like RON91/2/5 no point pump 97 just waste of money only...

most of CKD cars are made for RON91 due to thailand fuel... (Thai sell RON91) so inorder for your car to travel to thailand and not dying there engine is made to lowes regional requirement hence in South east Asia is RON91... this is also why before RON95 petrol pump sell minyak merah (RON92)

Some europe car uses min 95 cause based on europe region where min RON is 95...

Japanese performance car usually go around RON97-RON100 eg. Type-R is RON98... but RON97 can laaa any below will kill your engine...