There is a well-known "radius inflation" problem for low-mass main-sequence stars - especially those that are magnetically active and rapidly rotating (either because they are young or because they are in tidally-locked short-period binary systems).
This "radius inflation" means that magnetically active low-mass stars are bigger than they ought to be at the same mass. Thus, in principle, you could vary the levels of rotation and magnetic activity in low mass stars and this would produce a different locus in the mass-radius plot.
The result is that for stars of a given radius, the more magnetically active examples would have a higher mass. This can be a 10% effect for reasonable levels of magnetic activity.
Jackson et al. (2018); Garrido et al. (2019)
The radius of a main sequence star is age dependent, they get bigger as they get older. This is a very slow increase for stars with $R \sim 0.25R_\odot$, because their main sequence lifetimes are long. Nevertheless an older, slightly lower mass star could have the same radius as a younger, higher mass star. The effect is small ($<1$%) between ages of 1 and 10 billion years.
However, there is a larger effect in the opposite direction at younger ages because lower mass "stars" are in fact still contracting towards the main sequence at ages <1 billion years.
The radius of a star is also affected by composition. A lower metallicity star (at these low masses) will have a slightly larger radius at the same mass and thus a slightly lower mass at the same radius. The size of the effect is perhaps a few percent for a factor of 10 change in metallicity.