Anyone prefer horizontal bi-amping their monos?

So it really helps to know the configuration of your amps. Are they:

• True monoblocks: no switch to stereo mode, and cannot be used for vertical or horizontal bi-amp until you have 4 of them.
• Stereo amps with a switch to PARALLEL the L/R sides for mono operation: sometimes tube stereo amps offer this option, yielding up to TWICE the rated power output - like my VAC Signature 200iQ. In that case (200iQ), using a pair of amps in mono mode yields a HUGE performance gain over using a single amp in stereo mode. This is more of a performance gain than you’d get via bi-amping, IME.
• Stereo amps with a switch to BRIDGE (series?) the L/R sides for mono mode. Many SS amps offer this option and advertise up to FOUR times the power rating! There are a few downsides: you lose headroom for driving tough (low impedance loads). There is added circuitry for signal inversion (in worst case an opamp) that will negatively impact sound quality. In my experience, bridging sounds BAD. Worse than a single amp in stereo mode, unless you’re REALLY starving for power. Not recommended. In this case, you’d for sure be better off bi-amping with dual stereo amps, in either a vertical or horizontal configuration.

In my experience there can be some modest performance gains to bi-amping, but "proper" monoblocking is usually best. Also if you want to bi-amp, I'd recommend sticking to two IDENTICAL stereo amps or four identical mono amps. Mixing amps (even different versions of the same amp) gets real messy. 

If they are stereo amps, I would vertically bi amp them personally.

Ok everyone mebbe biamping isn't the correct word, thought it was. 

One amp for low end. One amp for mids etc. 

That's what my title question pertains to. 

You'll need two more amps.

Anyone prefer horizontal bi-amping their monos?

Yes! I have four true monoblock amps.

With bi-amplification both the Low frequency and high frequency portions of the system now have their respective amplifiers. That gives a reduction of intermodulation distortion. That said, active bi-amping horizontally, as I do, will give additional advantage from the elimination of lossy inductances in the low frequency portion of a conventional passive dividing network, and the result is significantly better amplifier damping factor, as seen by the low frequency driver. Active bi-amping is two notches above my passive crossover. See article below: Hope that helps Mike 😎

https://sound-au.com/biamp-vs-passive.htm