I ordered a model F2 Beam Extender from Visual Echos. I received the lens last night and had a chance to
try it out few minutes ago. This is on A700 with Sigma 70-300 Apo lens at 300 and HVL58 flash. I was about 25 feet away from the lamp shade and the lamp shade was in a dark room and the door to the room is ajar. The fit on HVL-58 is not very snug but good enough. I don't know how Minolta flash is designed but the rounded edged of HVL58 prevents a snug fit against the lip of the bracket.

With best regards,
Sury

With HVL-58


With Beam Extender and Flash in ADI mode:



With Beam Extender and Flash on Pre-flash TTL mode (recommended by Visual Echos)

I think you should compensate the shot either by changing the +/-EV of the camera or that of the flash (from within the camera).
The right exposure should be in between the second and the third.
Sury, I don't think the roundish edges of Sony/Minolta flashes are the problem, rather the manufacturer who plans everything on Canon/Nikon basis.

Dr. Harout,
I will experiment as suggested. The only difference between 2nd and 3rd shots is ADI v/s Preflash TTL. I guess a bit of learning is on the cards. When I pixel peeped the third one, I was amazed at the details of the lamp shade that was pulled
in. I was impressed.

Sury