Base size is not always a correct way to determine figure size even if all figures are the same scale.
Depending on the shape/stance of the figure, large figures might not need a large base if they are balanced where I have seen smaller figures that were on a standard trooper base fall over all the time due to the stance (centuars in MageKnight early on).
Some figures are so large that if they can fit down a corridor that 2 normal figures should be able to walk side by side down that same corridor.
Others are just long in body but narrow in width.
Take the Stalker figure, It should easily fit down any corridor that a human can but it should also take up to squares of space front to back.
If the Fiend can fit down Machine corridors then
Gremlins and runways can fit 2 per square because of their small size.
OK, to answer your question now.
No matter what the actual base size of the figure, there needs to be min square (or area of control in Planetstorm) for each figure.
1/2 square - Gremlins, runaways
1 square - PI, normal troops, machines, etc (or say that if the min is not listed in a figure's discription, it is considered a 1 sq AoC) and IMO, fiends should be 1 square)
2 squares - stalker *(special front to back),
BAP, Centurion, superfortress, Raptor *(front to back), are 2 squares side by side. meaning that if a corridor is not 2 squares wide then the figure can not walk down the corridor normally. They can fit sideways at double cost of normal movement.
Vehicles and the larger figures, I do not have in front of me, so that I can not list them. Even though they are normally only used in Planetstorm, a number of squares needs to be listed for each.
Here is how I see AoC working in both
LOS and Planetstorm.
Area of Control means that if any opposing figure attempts to pass you or comes with in the figures AoC that
HtH engagement happens. (Unless the figure is incapacitated).
With squares and LOS rules not much needs to be said about this as it is very obvious to most that this possibility happens.
On the table top though the number of squares equals the number of inches of AoC. So the Stalker and Raptor have 2 inches to their front (back) that they can engage and the typical 1 inch beyond their base to the side.
Other 2 square figures have 2 inches to their side and 1 inch to their front for AoC.
The bigger figures of course have a much larger AoC.
Vehicles do not gain this AoC unless they are the articulate ones.
Just some thoughts on your question.
Dave Chase
EDIT
Well, you two posted before I finished writing my post.
END EDIT