How is receipt date on manually entered PReq determined?

In SNP, I sometimes manually key PReqs into the planning book (SNP94). I key them in by entering a quantity at the receiving location, and then selecting a source/means of transport from the popup screen.

If I select a MOT with a shorter duration (e.g. airfreight), the PReq receipt date is changed to an earlier date than the date that I keyed.

It seems that APO is determining ship date based on a longer duration MOT (e.g. ship), and then adding the duration from the airfreight MOT to that ship date to determine the receipt date.

I want APO to respect the receipt date that I'm entering, but to use the shorter MOT that I've selected. Any suggestions?