Current IFISA strategy

If that is one of your biggest concerns then please, slow down a bit and read around these boards some more. The potential for capital loss far exceeds that of the difference in rates available. And to a degree it doesn't matter which platform you use at what rate, you WILL end up losing some money somewhere. If the platforms have priced things correctly then we'd expect it to be sooner at those with higher rates, and a lot lot later at those with lower rates, but here in the real world it'll never be that predictable. So expect it and plan for it.
If you want high rates you'll need manual investments in which case the safest way to do it is spread your cash over a lot of loans, and deal flows invariably mean you'll need multiple platforms to do this (so that you can cherry pick loans from each one, because accepting there will be losses isn't the same thing as blindly investing in every opportunity a platform presents). And given platform failure can and does happen it makes sense to mitigate against that as much as possible - it should hopefully not result in a total loss, but at the very least would likely lead to confusion and lack of liquidity for potentially rather longer than your original loan terms. In an ideal world perhaps you'd have enough platforms so that if one failed, that years interest from the others would cover your losses, but in the real world I'm not sure there's enough good platforms for that (I'm currently in 20, but it's nowhere near balanced enough). So personally I just restrict myself to an amount per platform that I could just about grit my teeth and shrug off if it all suddenly all became illiquid indefinitely.
It's not difficult to do if you're happy with spreadsheets etc, but if this has just given you a headache, may I suggest you look at Lending Works again