Probably Photivo is not a color managed program, because if it were color managed you would not see any difference no matter what space the image was in. Because it is not color managed you are not seeing what is really in the image. Also, WideGamut RGB is a very wide space, much wider than your monitor can display. In fact it is wider than even the best $5,000 monitor can display. Most monitors cannot display more than sRGB, which is a quite narrow gamut, but because that is what most monitors display, sRGB is the international standard for the internet and the color space that most print labs want.
Also you should be aware that editing WideGamut RGB in any bit depth less than 16 bits per channel can result in causing a lot of banding, especially in shadow areas and areas that should have smooth transitions within stretches of near solid color, like the sky. Photivo probably doesn't support more than 8 bits. I would advise staying well away from WideGamut RGB until you have a solid understanding of color management and a definite need to use such a wide space.