**Apologies in advance for the sketcher screenshots**

I have a fully defined sketch that has no unconstrained DOF according to the Abaqus query tool (Tools -> Query -> Detail). The outer arc is constrained to coincide on the quarter-circle construction arc. However, there are two possible solutions to this sketch (shown in the screenshots). When I edit specific dimensions, the sketcher will revert to the intersection solution, and a subsequent extrusion operation will fail. But, the coincident constraint between the arc vertex and construction geometry is still active, the sketch is fully defined, and there are zero unconstrained DOF. 

A few questions:
-Do construction arcs actually exist in Abaqus sketcher? I see that you can create construction circles, but not arcs. So, does Abaqus actually use the same construction circle backend for an arc, leading to this non-uniqueness?

-If construction arcs do not exist, is there any way to enforce a positivity constraint on a vertex (i.e., the y-coordinate of a vertex must be positive)? 
-Finally, I know this is a long shot, but are there any "best practices" when using Abaqus sketcher to circumvent these issues? I try to minimize the amount of dimensions in my sketches (typically, I only dimension features that I will be varying in future analyses), then constrain the rest of the sketch to satisfy these dimensions robustly. Is there a better way?