This should be balanced against "normal" armor, and thus not affect construction/point-costing in any way.
The theory is that hull hits in the first section are worth more than those in the second section, which are in turn worth more than those in the third section. (Because until you reach that first damage check, you have all of your weapons, your shields/ECM are at full-strength, etc., meaning your ship is more efficient earlier in the game.) So, you could think of a ship's "effective" hull strength as follows:
( 3 x HULL-1 + 2 x HULL-2 + 1 x HULL-3 ) / 2
Since all ships have the same split in hull boxes (33% in each section) there's usually no need for this equation (we're ignoring rounding here). Armor simply adds to the number of hull boxes in each section:
( 3 x (ARMOR-1 + HULL-1) + 2 x (ARMOR-2 + HULL-2) + 1 x (ARMOR-3 + HULL-3) ) / 2
If, however, all the armor is added to the first hull section, the equation becomes:
( 3 x (ARMOR-1 + ARMOR-2 + ARMOR-3 + HULL-1) + 2 x HULL-2 + 1 x HULL-3 ) / 2
Comparing an armor 12, hull 12 ship in "normal" and "front-loaded" versions:
NORMAL: ( 3 x (4 + 4) + 2 x (4 + 4) + 1 x (4 + 4) ) / 2 = 24
FRONT-LOADED: ( 3 x ( [4 + 4 + 4] + 4) + 2 x 4 + 1 x 4 ) / 2 = 30
In this case, front-loading increases the "effective" hull size by 25%. However, if you drop the armor by 33% (i.e. ignore one section of armor), you end up with:
NORMAL: ( 3 x (4 + 4) + 2 x (4 + 4) + 1 x (4 + 4) ) / 2 = 24
FRONT-LOADED: ( 3 x ( [4 + 4] + 4) + 2 x 4 + 1 x 4 ) / 2 = 24
Voila!