It’s good to compare these against Nepalese texts, but, there is no guarantee this is the same general recension of Buddhavacana. The original of the Chinese text could have had idaṃpratyayatā (or “this (idaṃ) hetupratyayatā” if such a thing exists, and I can’t begin to imagine what the sandhi would be), there is no way to know for sure, alas.
I mean, compare the Nepalese Lotus with Ven Kumarajiva’s. They are only vaguely the same on a line-by-line basis often.
And it’s not like Ven Dharmaraksa follows something like the Nepalese manuscript any closer. If anything it is more like Ven Kumarajiva’s.
This is less off-topic, now, but on the subject of odd Chinese recensions of Buddhavacana, the Tibetan Buddhāvataṃsakasūtra doesn’t mention Indra’s Net. Not once. At all. Back to topic.
So the Sanskrit & Chinese texts can’t always be used to evaluate one another. Particularly with the later literature.
We’re dealing here with Mahāprajñāpāramitōpadeśa here. A text whose various “originals”, likely in already-diverse lines of recension from the Indic strata before Chinese and later Sanskritizations, are very mysterious. The situation is very much the same with conjecturing at to the various recensions that Ven Kumarajiva et al surveyed when making their translations of the Lotus Sūtra.
The end of the Tathāgatāyuṣpramāṇaparivartaḥ alone attests to this. Look at the Sanskrit. Look at any of the Chineses at all, even predating Ven Kumarajiva. They are quite different.
At this point, I might inquire, what is the significant difference between idaṃpratyaya(tā) & etaṃpratyaya(tā)?
As I see it, by your metrics, 是因緣 may already be “proven” to mean etaṃpratyaya(tā), according to those above dictionary entries.
I am so unscholarly and unbeholden to peer review, as well as amateur enough at Sanskrit to be daring beyond my abilities, that I can suggest things like
(ity) utpādād (vā) tathāgatānām anutpādād
(vā) idaṃpratyayatā dharmatā [some Sanskrit here we can just imagine] lokadhātvām [just to pick a case, for the sake of it, apparently this word doesn’t even exist]
Or etaṃ pratyayatā for 是因緣 if the difference is that significant.
Things in the above might not make sense. My Sanskrit isn’t that good. But the main point was the idaṃpratyayatā dharmatā sequence for 是因緣法相