Which is better lateral or vertical bi-amping?

I have heard that vertically (each amp feeds the low and high of one channel) makes more sense, since there will be more headroom than if one amp handles just the low frequencies. On a deep bass note, in a horizontal arrangement, the bass amp will be driven hard, where the mid/tweater amp will be "loafing". Of course, many people will use a S.S./tube bi-amp configuration. Naturally, a horzontal arrangement (tubes on the tweaters) is used!

Chazz,
Listen to your system both ways and see which sounds the best. I'm assuming both amps are identical from your comments.

It seems that a lateral configuration would minimize any character differences in your amps from the right to left channel. This should not be a problem with high quality same model amps but something to consider.

Chazzbo and Griswold, offer the best arguments while Fatparrot's suggestion would certainly be worthy of consideration with lesser amps. Ideally 4 mono amps carefully calibrated would be ideal for bi-amping. Due to a less extreme frequency demand there would be less electronic gymnastics and inertia from impedance loads ,etc., running laterally. With better dual mono stereo amps one channel couldn't pick up the slack of the less demanding frequency requirements. Of course the all mono or to a lesser extent dual mono amps offer better seperation and consequently less cross-talk.