I've been dealing with this for years .. and that is the size of the jpg output which seems to be fixed at 95%. I don't see any way to change this to 100% as a default. Instead I have to reset it every time I do an export. Gets tiring...and annoying. I've looked all over in the app and don't see any way reset the size so it sticks --- permanently. Either it's not there or I'm just not looking in the right place.
Btw -- I'm happy with version 12. Have looked over the improvement offered by Version 13 and don't see anything that impacts me. In the meantime, I sing the praises of PTGui to anybody I talk to about my photography.