Soft seat wafer butterfly valve

For soft seat wafer butterfly valve, can the connecting flange on piping be a slip on flange? The valve vendor suggests to use special flange for soft seat wafer butterfly valve. Can we use weldneck flange instead of special flange?

Here is a picture. The small end connects to valve, the large end to the pipe:


It looks like that the “special” flange is a modified “SW” joint with a larger size. It seems that there is no interference issue of the valve disc to the pipe ID.
Instead of “special” flange, IMO, the standard WN flange per B16.5 is a correct design for this application, if the slip-on flange is not suitable for the operating condition.

Above is a snippet.