Printing a #10 envelope: is LO fixating on "Printer Settings?"

Not being satisfied with the flexibility of Insert->Envelope, I determined to print an envelope as a separate document.

Like so many others I found that my carefully prepared “envelope document” (which I had formatted as a 4.13Wx9.5H page with two rotated “text boxes” containing addressee and return addresses) was being sent to the printer with instructions to print on “Letter” sized paper.

File->PrintPreview looked fine.

I’ve noticed in the File->Print dialog that LO believes that the document size is “Letter.”

The center-fed envelope emerged blank, which it would if the printer was told to use Letter-sized paper and printed the envelope left-justified.

I have confirmed that I can change this through the File->PrinterSettings->Properties dialog, but only to a relative few alternatives, none of which is “#10 envelope.” (Interestingly, the same dialog appears through File->Print->Properties, but with PaperSize and Orientation then greyed-out/disabled.)

My question: is there some way of adding other PaperSizes to the PrinterSettings dialog?

I have been able to get around this by File->ExportAs->PDF and then printing from a PDF viewer (‘evince’ on Linux).