Mostly just to add to my previous comment, but the original invading clans used invasion corridors roughly 2% the circumference of the Inner Sphere. If you were to use the 33% attack estimate, using all invading clans, you'd be looking at 2.5% each, 40% a bit more than 3% each, and 49% (roughly where a straight line along the border from a jump out of Terra equates) ~3.75% each. The second and third options are a significant increase in the width of the attack corridors - and the original invading clans tightened up really really quick (if you were to aim at a point where the outer lines merge you'd be looking at either Gram or Shimosuwa, or thereabouts - this is ~2/3rds the way to Terra).