So how do you get a motor to stop part way between its natural step positions.
Put equal current thru each phase?
I suppose you can consider that the motor coils "work[ing] against each other" but I would consider it more as the two coils working together.
But to return to the OP:
Can I get a different motor with a different resistance that will get me closer to more accurate microsteps?
The people who care about microstepping accuracy are the 3D printing people. Because inaccuracy shows up as weirdness on their high-resolution 3D prints.
If I needed accurate microsteps, I would find out what motors/drivers the 3D people are using. I don't offhand know what combinations are working for them, but I have seen online discussions about it.
What is your application that depends upon accurate microsteps?