[Riftmaker]

Okay...opened up the PH...and it says:

9*10 = 90 (total hit dice for fighter class).
10*4 = 40 (total hit dice for mage class).

40 + 90 = 130.

130 / 2 = 65.

9*4 + 2 = 38 (total con bonus. Period. None of this each class has its own bonus stuff)

65 + 36 = 103.

If the game really divides post max HD hp by 2, then it should be (15*1) + (10*1) (fractions round down) = 25.

103 + 25 = 128.

If it doesn't, then it should be:

(15*3) + (10*1) = 55.

103 + 55 = 158.

My conclusion is that the game uses some gimped form of HP calculation, as the PH says that you take the highest CON bonus, and divide it between the levels, regardless of what the other one is.

So, at character creation you'd get +4 hp, and every time you gained a level in either class you'd go: (hdroll / 2) + (highestconbonus / 2) = total hp gained.

So, because you tested this in the game, then I concede that the HP rolling in the game is messed, and not your math.