My personal experience is of having seen the ARRC, MNDSE in Iraq and having spent 10 months with the Kabul Multi-National Bde.

I am in two minds as to whether it is the size or the construct of the HQ which matters most.

My experience is that where there is a lead nation then individual augmentees can slot in and the system works well. At Div and Corps where I have seen this happen it has worked very well. In MNDSE in 2005-6 it was the multinational augmentees that kept the ostensibly British HQ MNDSE afloat!

Where there is no lead nation or where the number of multinational augmentees is larger then 1/3 then national sensitivities start to cause a lot of friction. I think that bde HQs, despite their burgeoning size are still too small to allow a great degree of multinationality; the friction outweighs the benefits.

Common doctrine and language is one thing, but equally important when looking how these things work is what we call 'MSCOM' (Military Secretary Command) ie: who writes your report and does it count...