Cannot assign payroll elements configured as percentage during Hiring

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Hello experts,

we configured payroll elements both as percentage and amount. When performing Core HR transactions (i.e Hiring; Promotion), it is possible to assign payroll element in the Additional Compensation section only if included in individual compensation plan but in these plan just payroll elements configured as amount can be assigned. Our customer wants to assign also payroll elements configured as percentages, but in turn they cannot be added in individual compensation plan, so they cannot assign them at this moment.

Is there a way to assign payroll elements configured as % in Core HR transactions? If so, how can we do it?