Travel expense form shows mileage flat rate as receipts paid by company

The travel expense form shows mileage (e.g. 180km = 54€) as "travel flat rate" and in addition as "sum of receipts paid by company" (please refer to the attachment). This sums up to 108€ as total cost of trip while the real cost is only €54.

I am looking for the customizing option to prevent the system from calculating "sum of receipts paid by company".

Any hint is highly appreciated.

Thanks in advance,

Wolfgang