920GB/s bandwidth is required to achieve 115MH/s theoretically. That's 23GT/s.
In reality though, the efficiency is about 85-90%, so you'll need 25-26GT/s to get 115MH/s. So its possible on the 3090, but not on the 3080.
Compare it to Polaris.
32MH/s requires 256GB/s bandwidth theoretical. 256GB/s bandwidth needs the memory clocked at only 8GT/s. But user results show they need the memory to be 8.8, or even 9GT/s to reach that. This is all assuming you have the optimal timings.
It's unrealistic to expect 115MH/s. They are liars. Not surprising from China.
Okay, let me try to understand it, given your numbers, if 32 requires 256, 64 will require 512, 96 will require 768, and last, 128 mhs will require 1024 gb/s.
3080 --> Bandwidth 760.3 GB/s, so in theory the maximum it will reach is 95.2 mhs, a little below 96 mhs which need 768 gb/s, now when they overclock the memory, that 760.3 gb/s increases, so lets do the math, 19 Gbps * 2 * 320 / 16 = 760 GB/s, 1188 * 8 * 2 = 19 gbps, now if we get that memory overclocked to 23gbps, which if we think about is 20% memory overclock, which is very possible, 23 Gbps * 2 * 320 / 16 = 920 GB/s, if we calculate 1024 / 128 = 8, so we need 8 gb/s to get 1 mhs on eth, so 840 / 8 = 105 mhs, so basically a 3080 need 115 x 8 = 920 gbps to get 115mhs. Is that impossible? no, but it needs 20% memory overclock. So 115mhs on eth is very much possible.