Hello
I'm on SW 2017.
I've been searching for hours on how to foreshorten this dimension, but no luck.
Some of the methods I've done:
1) enlarge Detail B, then chose the dimension I need, then reduce the detail circle (which is what is in the picture below)
2) I right clicked the dimension line, hoping there would be a foreshorten option, but no.
3) In document properties, made sure all foreshorten options are checked under "automatic"
Introduced in SOLIDWORKS 2016: 2016 What's New in SOLIDWORKS - Foreshortening of Linear Dimensions
Foreshortening of linear dimensions should be automatic for detail views. You simply select the model edge in our detail view and then select the model edge on your parent view. Also, linear diameter dimensions have always been forshortenable in detail views, so the newer method is much easier to use.
I'm not sure why your example is not working. Since the functionality exists, it might be a good idea to contact your reseller, even if you are on SW2017.