I've been working on a new diffuser (just finished it tonight) and experimenting with the position of the flash heads a lot lately. I like to use them in a key and fill orientation (key at the top, fill off to one side). I've pretty much convinced myself that I'm getting the best results with either both flash heads mounted directly to the flash mount that Canon supplies with the MT-24EX macro twin flash, or with the key elevated on a cold show (Kaiser Adjustable Flash Shoe).
The first three images were taken in the field, and the last in the "studio" (patio table).
Tech Specs: Canon 70D (F11, 1/125, ISO 200) + a Canon EF-S 60mm macro lens with 25mm of extension + a diffused MT-24EX (flash head "A" set as the key and "B" as the fill). These are single, uncropped, frames taken hand held. Technique: I cut a Zucchini flower, taped it upside down to a leaf, and then injected artificial nectar into it. I used the flash to expose the subjects and natural light to expose the background.
A male Banded Eye Drone (Eristalinus taeniops). Male because its eyes are touching (females have a gap between them).
Tech Specs: Canon 70D (F11, 1/60, ISO 200) + a Canon EF-S 60mm macro lens with 37mm of extension + a diffused MT-24EX with head "A" set as the key and head "B" as the fill. This is a single, uncropped, frame taken hand held.
Technique: I injected the flower with artificial nectar to give the critter a reason to let me get close. [IMAGE'S LINK: https://flic.kr/p/zHhKp5]Finger Licking Good by John Kimbler, on Flickr
Coelioxys sp. Leaf Cutter Cuckoo Bee
Tech Specs: Canon 70D (F16, 1/250, ISO 100) + a Canon MP-E 65mm macro lens (around 2x) + a diffused MT-24EX. This is a single, uncropped, frame taken hand held.
Technique: I went looking for dormant bees early in the morning and found this Cuckoo Bee sleeping in my Lavender. After it woke up I placed it next to a Daisy and it went back to sleep. I used an artificial flower behind it to keep the background from being black. [IMAGE'S LINK: https://flic.kr/p/zzcgz2]Sleeping Cuckoo Bee by John Kimbler, on Flickr