Ohmmmmmmmmm

[goldstone]

Why do I need to move the fader on my new head unit significantly toward the front speakers [+5 on a scale that runs from -7 to +7] to properly balance the soundstage in my '89 420SEL?

Facts

1) No fader or external amps in use (I bypassed the stock setup and connected 4 new sets of speaker wires directly to the speakers);

2) Stock speakers (all in great condition);

3) Head Unit has a 4x25W Max output internal amplifier;

Assuming the amp in the head unit is okay, I suspect it has something to do with resistance and sensitivity of the front drivers vs. the rear, but I just don't understand enough about the electronics to quite figure it out... yet!

For those not familiar with the '89 126 speakers, the rears are comprised of 6.5" drivers flanked by two 1" tweets each (total of 6 drivers). I'm assuming they're 4 ohms, but I haven't removed them to check (anyone know this for sure?) The front doors contain a 7" sub rated at 2 ohms, and the dash has a one-way 4" speaker rated at 6 ohms.

So, if I probe my very limited electronics knowledge, Ohm's Law tells me that the front components (which are connected in parrallel) create [1 / (1/6 +1/2)] or 1.5 Ohms of resistance in total. And, if indeed the rear drivers are all 4 Ohms, then they should present [1 / (1/4 + 1/4 + 1/4)] or 1.333 Ohms of resistance.

Does this small difference in resistance explain the reasons for needing to shift the fader so far front to attain proper balance, or is it something even more arcane