ya know, I was curious so I did the basic google work that the OP should be able to do on his own. Apple lists the pixel dimensions and ppi on their website. Quick math tells me that the 12.9 is 10.35 inches wide by 7.76 inches tall and the 11" iPad is 9.05 inches wide by 6.32 inches tall.
Then a quick google search brought up this site
https://www.projectorscreen.com/projector-screen-calculators
and I was able to enter in the screen sizes to get this comparison of what a 16:9 video would look like on each screen:
View attachment 819334
So there you have it. When you are viewing a 16:9 aspect ratio movie on the 12.9, it will be 1.3x larger than on the 11"
[doublepost=1548976017][/doublepost]its funny how the 12.9" screen is barely 1.25" wider, but a 30% increase in viewable movie size.
Personally I far prefer the 12.9. it really does make a more immersive 1-person movie experience. I have no need for a huge 4k TV thanks to my iPad