Each path segment needs to be a minimum of your rounding value times 2 in length.
InDesign takes the rounding value and applies it to each end of every path segment. That means for 1p0 rounding on a horizontal path, InDesign assigns 1p0 to both the left and right end of the segment. Meaning the minimum path segment length, to retain the 1p0 rounding, is a 2p0 segment.
Shorter segments will use the maximum rounding possible. If the segment is not 2 picas long and rounding is set a 1p0, then instead of using 1p0 for the rounding on each end of that segment, InDesign will use the segment length/2 for rounding. This results in inconsistent rounding.
InDesign does try and favor the rounding value, So if a corner has a single shorter side segment but it's above the rounding value, InDesign will round one corner at the value, then "short" the other corner the remaining length of the segment.
End anchors assume they need the same 1p0 of the rounding value even if there is no rounding on the end anchors. So a 0p6 long segment really only allows for a maximum of 0p3 for rounding at each end.