how to avoid Invoice Split due to billing date, reference number and payment reference?

Hi,

In a scenario of delivery to invoice copying, we are facing issue of invoice split.

After analysing split, came to know that split happened because of different billing date, reference number and payment reference.

In VTFL we kept below fields blank at header level:

Assignment Number

Reference number

In VTFL we kept below setting at item level:

Copying requirements: 001 (this is a del related Pro-forma invoice)

Data VBRK/VBRP: 001 (Inv.split (sample))

Also in VF04, at "default" tab maintained billing date, but still system is splitting invoice.

Split analysis showing below results

Different billing date

Different reference number and

Different payment reference

Pls let me know how to avoind this split. Do we have to copy routine and do changes into it to avoid split.

Regards/Pravin