Personally, the only obvious issue Id see with mast plus var is the possible impact on hair. Ive stacked multiple dht's and had no overt negatives (didnt negatively impact gainz, or libido, etc). I mean, what difference would there be increasing the mast and dropping the var? My point is that combining dht's is not necessarily asking for issues, esp when the combined dose could be run solely as mast (know what Im getting at?) The other thing is, yes dht's share some characteristics, but they are still unique in other respects.
I tend to always run mast at least the same as test, if not higher. Again, I have never seen negatives appear with increased doses.