Explain the internal field effect within the Machian MOND proposal

Explain how the internal field effect—whereby large internal accelerations within a composite system do not suppress the MONDian motion of its low-acceleration center of mass—arises within the proposed Machian inertial-drag framework, rather than assuming the center-of-mass horizon prescription resolves it.

Background

The paper derives MOND-like modified inertia from Sciama’s inertial induction and gravitoelectric effects in a constant-Hubble expanding universe. The acceleration-dependent causal horizon is applied to the total acceleration relative to the cosmic inertial frame, which provides a proposed explanation for MOND’s external field effect.

The authors distinguish this from the internal field effect, in which a composite system’s internally high accelerations should not eliminate the MONDian behavior of its low-acceleration center of mass. They state that their proposal does not presently explain this phenomenon and only suggests using the center-of-mass acceleration in the horizon prescription.