Jacinto bought a dual mount for a Varia and a Cygolite that goes on the back of his rack where the holes are that a reflector would mount. Some racks have two holes, some have three. There were a variety of mount styles. 

He was having trouble with the  Varia giving false notices. Now, it works perfectly, on the very end of the rack, with absolutely nothing behind it. 

Jacinto bought a dual mount for a Varia and a Cygolite that goes on the back of his rack where the holes are that a reflector would mount. Some racks have two holes, some have three. There were a variety of mount styles. 

He was having trouble with the  Varia giving false notices. Now, it works perfectly, on the very end of the rack, with absolutely nothing behind it. 

I have a Specialized Stix light there, mounted horizontally so it's less than an inch tall.  There is barely clearance for that so no way a 4-inch tall Varia would fit.