MOGRT file comp settings not exporting correctly

Your MOGRT should have the same frame size as the AEP comp that was used to create it. A copy of After Effects will open in the background to render the graphic in Premiere in the same way a Dynamically linked comp works. There should be no change in the frame size.

When I design for social media, I set up a large square comp and include an Expression Controls/Menu Control to resize all of the elements for horizontal, square, and vertical sequence sizes so I don't have to load up a half dozen of the same graphics in Premiere Pro. I have created a Shape layer set as a guide layer to preview all of the title safe areas in the comp. It might be a better workflow for your project.

Simple if/else expressions adjust the size and position. Here's an example of the position expression tied to the Menu Control:

ctrl = thisComp.layer("Control").effect("Comp Size")("Menu");
if (ctrl == 1)
	p = [1080, 1500]
if (ctrl == 2)
	p = [1757, 1453]
if (ctrl == 3)
	p = [1456, 1500]
if (ctrl == 4)
	p = [1757, 1453]
if (ctrl == 5)
	p = [232, 1932]
if (ctrl == 6)
	p = [2000, 1800]
fix = thisComp.layer("Control").effect("Position Offset")("Point");
p + fix