Not trying to prove that it is better…but to prove that what you said about a 150mm is as I said…false/bad info…
Yes - I still think that. They are more likely to run away during the day and so the added working distance is a bonus during the day. Often the ones that sit down do so on flowers, which give plenty of room to manouver around.
On the other hand, the shorter focal lengths are easier to handle and smaller so it is easier to get into some of the cramped spaces, where they tend to hide. It also often allows putting left hand so that it is supported by what the target is sitting on and at the same time supports the camera. With a longer objectives that doesn’t work. And during the the night the don’t spook so easily … unless you want in-flight pictures on/near flowers. For that longer is better.
All that naturally depends on what you shoot and what other equipment you use such as tripods or external flashes.
I use the left hand technique all the time because most of my shots are hand held…so your theory on that is not correct either…and the added distance helps whether day or night.
The lens are the same or close to the same diameter at the front element, so getting into spots is not that much of a problem any more or less than with the shorter lens…another plus in that situation is the added working distance…it affords you to not have to get into the tight spot because you can shoot at a further distance and still get great shots.
I use an external flash most of the time with a diy diffuser and I also have the Venus KX-800 dual flash unit with a diy diffuser…both diffuser setups are arranged so that they do not protrude into the working distance of the lens and can be quickly adjusted if need be.
For moths on sheets, which normally do not fly away when you get close, I really like the Canon 60mm macro. It is relatively inexpensive and the autofocus is excellent–usually right on the money if you have sufficient light to focus. The shorter working distance actually makes getting a good angle easier when working on a sheet or other fixed surface. If you need more than 1:1 magnification, an extension tube will give you quite a bit with the short focal length.
I’ve been using the Sigma 105mm Macro on several Canon bodies for years and have been very happy. The 105mm lets you stay back a little more for skittish bugs. Plus you can buy extension tubes that let you get closer and higher magnification.