Primary logos are automatically re-scaled to 256x256 px and alternate logo at 128x128 px. Use that size as a template and take up as much of the space as you can.
In your case, set the bobcat to primary and M to alternate. There is currently a bug where no matter what size you set the field logo on the teambuilder site, it will revert to small in-game.
This is what I did for Montana State a couple years ago.