Cannot feed 13x19 paper on Pixma Pro-100 from rear tray

[snap01]

I'm trying to feed 13x19 paper into my printer from the rear tray (which is actually on top of the printer as opposed the the "manual feed" which is at the back). But it doesn't seem to work. I get one of two errors:

First, if I set my paper size to 13W x 19H and then go to the print settings dialog (Quality & Media tab) and I select the rear tray option, I get the following error message "A paper size that cannot be fed from Rear Tray was selected." It then tells me to select the "manual feed" option. I can't leave the dialog without changing to manual feed.

Second, If I set my paper size to 19W x 13H I can select the rear tray option. But when I go to print from the rear tray, it prints the image as if it were only 8.5"x11" (image is truncated).

I'd really like to use the rear tray due to space reasons.

I'm printing from Lightroom 7.3.1, on mac / high sierra with canon driver 16.20. Printing over WIFI using IJ Canon network driver.

Printing 8.5x11 seems to work from the rear tray fine.

Any ideas on what's going on. This is driving me crazy.

[snap01]

Apparently the driver sets a limit of 12.95" width for the rear tray. With 13" wide paper the driver forces the use of the manual feed. Some people have suggested to just use the A3+ setting.

[jrhoffman75]

A3+ paper is nominally called 13x19, but it really is 329mm wide, which is 12.95 inches.