You can use constant valuation using V_T539J. For each country group, configure this view with valuated w/t = say 2001, base w/t = the w/t of basic pay and the corresponding percentage for the country. Copy the line for the other w/t's required for the country group.
In V_T511 configure the w/t's as percent and indirect val.module = PRZNT.
When you enter in IT 8, pay scale details and the basic pay w/t in IT 8 and press enter, it will show the corresponding value from T510. Depending on the basic pay w/t's config in V_T511, the payroll user would be able to modify or not this amt.
When you enter the other w/t's as above say 2001 and press enter, the PRZNT module will calculate the amt for this w/t based on V_T539J config.
This should be enough for your requirements.
If you have other requirements e.g., prorating, the V_512W_D requires for these w/t's proc cl 10 to have a similar non-zero value as for basic pay.