I would think that the wearing of the uniform of dragoons was a matter of individual choice to the General Officer. If he war a General Officers uniform with a bicorne he would of course be more conspicuous in action and thnerefore a clear target for those wishing to take out senior officers. I believe there was a regulation circa 1806 stating that the cuirass was to be worn by general officers of heavy cavalry. d'Hautpoul,Nansouty are often illustrated thus as are other cuirassier generals. Sometimes they wear the bicorne and sometimes the helmet. Kellerman is illustrated at Waterloo wearing just the regulation general officers uniform when unhorsed at Quatre Bras.Ornano is illustrated in a Dragoon General's uniform in various books as is Letort. I wonder if there are any first hand descriptions of these generals on active service on the battlefield?