Hello
The term of "mixed formation" used by the French in wwI is not the notion of mixed formation as we (or at least I) usually use it.
Most of the time, a "mixed formation" of bombers is a formation of bombers of different types flying in respective fixed positions in order to benefit from mutual protection.
This was not exactly the case, actually, a better word would be "close escort" as the R11 were moving around the Breguet formation so as to position between the ennemy fighters and the bomber they protected.
In FE2 words, an "escort mission" would be good to descibe how they behaved.
This is clearly outdated, as more archives where made available that improve the view we have of the R11 career :
For instance, the mission described there :
Was the only publicly available account of a R11 mission for years.
Now, lot of reports are available for periods from May 1918 to the end of the war outlining that when escorted by R11, bombers suffered less casualties and were more accurate in bombing.
Still, the efficiency of the R11 is a valid question, but the above mission is absolutly not representative of the R11 career. It would be a little as if we judged the TBM Avenger based only its performances at Midway !
There are also accounts of Caudron R11 missions here :
(available there : http://www.asoublies1418.fr/index.php/cahier-des-as-oublies/la-guerre-du-ciel-1914-1918) : This collection is basically a recollection of various french army reports, archives and personnal diairies
On 6th of October, a first mission of 1 recon + 3 protection R11 was met by Fokker D7 (8 according to french archives) :
One Caudron was damaged, another was shot down, the mission was a partial success, but a second mission the same day (escorted with Spad this time) was a success
In Icare N° 213 : Journal de Jules Abel [1] 1916-1918 : pilote de reconnaissance, Jules Abel flies a R11 as artillery spotter for quite a short time as "gotha" bombed the airfield and put out of action most of the unit's Caudrons
In Fana 535, they were used as "picket" patrols (translation for "guet", the plane had to give a warning when some enemy planes crossed the line), in groups of 2 or 3.