Firstly, Delta is known to be a bit 'finicky' about exposure. Maybe FP4+ or HP5+ would give you a bit more latitude. Unless you're looking for very large print sizes then ISO400 film should be OK.
Second, I looked at your Flickr shots and they're nice, so nothing basically wrong with that lighting setup - did you used the same one! If you didn't, go back to what you know worked while you sort out any other issues.
The Koni has a leaf shutter, so no issues with curtain lag. However, it does have M and X settings for flash. Was it set on X sync? Makes a big difference. Was the shutter speed set at the camera manual's recommended speed for flash sync? Not all leaf shutters sync at every speeds - I don't know about the Koni but maybe it only syncs at one or two speeds like some other cameras.
You mention using a meter, but is it a flash meter, and did you take the reading at the position of the subject? If not, the exposure indicated is going to be way off. A reflectance or incident meter of conventional type won't cut it. Sorry if I'm pointing out the obvious and you've covered all those bases but you didn't give any real detail about the metering or the flash sync settings you used, and I think that's most likely where the problem lies.
Oops! I've assumed you're using flash, having referred to 'monobloc'. If you're using tungsten studio lighting then most of what I've written is irrelevant!