You don't say how you feel with and without the Adex, but if your goal is just to stay at 15-25pg/mL E2 when bumping to 300mg/week and you know reliably from ulltra-sensitive testing that you really are at 15-25pg/mL E2 with 0.25mg E3.5D of Adex at 160mg/week, I would add 0.125mg E3.5D for a total 0f 3.75 E3.5D of Adex.
I think E2 doesn't follow a linear increase relative to dosage, so this should get you relatively close without the risk of crashing you. If it's not enough after you run an E2 sensitive test or you can feel symptoms coming on, you can add another 0.125mg E3.5D. But I wouldn't just double the Adex right off the bat. At 15-25pg/mL you're pretty close to crashing your E2, and if you do it might ruin your cycle or at least part of it.
Personally I would say don't add any more Adex until you get symptoms, you might find that you feel a lot better with some additional E2. I'm not at all anti-AI or a proponent of letting E2 skyrocket, but if 0.25mg E3.5D got you hypothetically to 30-40pg/mL E2 on 300mg/week of Test, I think that might be healthier for you than staying at 15-25pg/mL.
Not much of a believer in the idea of a fixed ratio either but I think there's something to the idea that you don't want to stay at 15-25pg/mL regardless of Test levels. E2 should probably follow Test to some degree, although I don't think the ideal relationship is linear