What you want IINA to do:

When Text Size is increased causing the OSD overlay to get wider, the progress bar should also extend across the new width of the OSD overlay area.

What IINA does currently:

If I set the OSD text size to 40 pts the progress bar stops a little less than half way across the OSD area making the full video progress feel like it's only half way.

Why you think this should be added:

It would feel more correct as a progress bar to extend across the area. Right now it just seems to end early at a glance it's unclear by progress bar how far you are actually through the video.