Philippe,
Your link takes me to a page with a too-small image to interpret much detail, but from what I can see, you appear in the larger bloom to have shot in diffused portraiture style with a slice of sharp focus but no attempt made for sharp near-far DOF. That's a perfectly good style which is more pictorial and not as literal, but rather beyond the realm of what I was addressing with traditional macro work. Your use of a MF lens is interesting but without knowing whether you were covering the entirety of the 4x5 sheet with the Planar would be harder still to interpret. But let's see if any of the following clarifies my point with you.
There are sharpness limits imposed by stopping down due to bending light around that distant pinhole of light created by the iris AKA the aperture. Macro work not only requires greatly stopping down for adequate near-far depth of field but also adds to this distance with the additional bellows or helix extension beyond infinity focus to get to 1:1 magnification ("life-size"). The effective aperture at 1:1 will be two stops smaller than the marked aperture at infinity with any symmetrical lens design. Now further add to this that large format lenses due to their longer equivalent focal lengths, worsen the already shallow macro DOF issue due to telephoto effect. So LF requires stopping down considerably more, to get the same DOF result as can be achieved in smaller formats, several stops more for the same FOV lens equivalent. By an effective f/32 severe diffraction limits will start to be encountered. With LF macro it'll be a challenge to stay within these limits whenever photography three- dimensional objects if movements don't help address DOF..
Yet for all the extra bulk, film cost, and hardship, you'd think 4x5 should still give you a much better final image because the bigger neg won't require as much enlargement, right? Well, frankly, no-- not at the original poster's specified 1:1 repro ratio. On film this is exactly the same life-size image regardless of format, and will require exactly the same degree of enlargement for the subject matter to appear at the same size on the final print . True you will get a larger field of view at 1:1 with large format, but to get the same size flower blossom in the final print you'd be blowing it up just the same whether the original was shot on a roll of 35mm film or an 8x10 sheet.
At 1:1 and beyond we're getting down into the magnification realm where LF has not only lost any natural advantage, it has, in fact, become a liability. There's really not much call to use large format for true macro.
Medium format and especially 35mm macro lenses at this repro ratio are significantly sharper to begin with (astoundingly so) and won't suffer diffraction limits to nearly the same degree as LF because they'll be shot at effective taking apertures that are wider to get the same DOF. I'll make an educated guess that the nexus of where absolute film limits meets absolute best available macro lens would test out between 35mm and 645, rarely 6x7 and will be dependent on many variables such as the resolving power of the particular film and development, and how small an aperture is needed to get adequate DOF for any given subject. In other words, a moving target, depending on how flat or 3-dimensional the subject.
None of which has yet addressed the inconvenience factor of the larger formats, and the outlandish extensions required for macro that become impractical or downright prohibitive beyond the studio. There are the practical considerations with shooting macro, like shutter shake. At the extremes of focal lengths, smaller formats do have distinct advantages; it's always more practical to shoot macro with more DOF available, less flash power, less reciprocity-falilure compensation, less overall extension, smaller tripods, etc.--benefits that smaller formats will afford.
