[Some thoughts inspired by Shamik's recent talk 'On the Plurality of Grounds'...]
Suppose comparativism about mass is true, i.e. "the fundamental facts about mass are facts about the mass-relations between things". Absolute mass claims, such as that my laptop is 2 kgs, must ultimately be grounded in mass-relational facts, such as that my laptop is twice as massive as the standard kilogram weight in Paris. Of course, no single such relation suffices: the standard kilogram might have been twice as heavy as it actually is (in comparative terms: mass-related to the vast majority of other objects at double its actual ratios), in which case the aforementioned relation would imply that my laptop was 4 kgs rather than just 2. So the full ground of my laptop's being 2 kgs must instead be massively plural, perhaps depending on the entire universe of comparative mass facts.
At this point, Shamik worries that the universe of comparative facts can't ground the single absolute fact about my laptop's mass, because it includes facts that are (intuitively) explanatorily irrelevant. For example, the mass relation between my laptop and some particle on Alpha Centauri seems irrelevant to my laptop's being 2 kgs. Shamik's solution is to introduce plural grounding: no single absolute mass fact has a ground, but the set of all such facts is plurally grounded in the set of all relational mass facts. Neat enough, but I wonder whether we should really accept the intuition of explanatory irrelevance that prevents us from simply grounding each individual absolute mass fact in the set of all relational mass facts.
Granted, the mass relation between my laptop and some Alpha Centauri particle clearly doesn't play an especially central role in the explanation of my laptop's being 2 kgs. But if we accept comparativism, I don't see the basis for insisting that this relation must play strictly no role at all. After all, it's pretty natural to interpret comparativism as a radically holistic view. For example, it's not enough even to look at all the intra-Earthly mass relations -- if those all stayed the same, as did strictly extra-terrestrial relations, but extra-terrestrial objects were all doubly mass-related to terrestrial objects, I take it that this is most naturally described as everything on Earth shrinking, rather than everything else in the universe doubling in mass. (Not that these are really two distinct possibilities, according to comparativism. But the point is that all the local mass relations, that in the actual world partially ground my laptop's being 2 kgs, would in this scenario instead ground my laptop's being 1 kg.) Given such an holistic picture, it seems natural to say that every part of the whole -- every mass-relation in the universal set -- is at least slightly relevant. After all, if the mass-relation between my laptop and the Alpha Centauri particle, along with a whole lot of other laptop-ET mass relations, had been halved, then my laptop would weigh 1 kg rather than 2. So that fact that all of those laptop-ET mass relations aren't halved is explanatorily relevant to my laptop's weighing 2 kg after all.
As an analogy, consider semantic holism: the view that the meaning of a word is fixed by the totality of our dispositions regarding its use (rather than by any privileged subset of 'analytic' inferential dispositions). One could go Shamik's way and say that this is a case of plural grounding, whereby one's entire vocabulary set (as a collective) is grounded in one's total set of linguistic dispositions. But has anyone ever thought this necessary? (I'm totally unfamiliar with the relevant literature, so that's a genuine question.) I would've thought that most people would be happy to allow the semantic holist to say that each word's meaning is (individually) grounded in the totality of their linguistic dispositions. And if that's right, presumably it's legitimate for the comparativist to say the same sort of thing about the holistic grounding of absolute mass claims in comparative mass relations.