Why do you believe that? Are you writing from theory or from experience? If experience, please tell us more.
Originally Posted by AgX
I ask because in my experience (55/3.5 and 55/2.8 MicroNikkors, 105/4 and 105/2.8 MicroNikkors, 135/2.8 MakroTeleQuinon, and 200/4 MicroNikkor AIS) ror handheld closeup work with flash around 105 mm is the best compromise, taking into account ease of handling, working distance, live subjects' minimum approach distance, and so on.
I've watched one person try to use my portable photographic aquarium with a 24 mm "macro" lens on a 35 mm SLR. Having had the joy of watching it done, I'd never ever use such a rig for closeup work.
Ive tried to shoot a 25/3.5 Luminar on a Minolta Compact Bellows on a Nikon. Short version, handheld much above 1:1 is a waste of effort.