My main reason for trying to be mostly risk-neutral in my donations is that my donations are very small relative to the total size of the problem, while this is not the case for my personal investments. I would donate differently (more risk-averse) if I had control over a significant part of all charitable donations in a given area. In particular, I do not endorse double-or-nothing gambling on the fate of the universe.
You make a good point that OP is more likely to make judgements regarding small donation opportunities, so I’ll have to revise my position that small donors should specifically seek out smaller organizations to donate to. But the same argument for “topping up” OP donations could equally be made to support simply donating to an EA fund (which I expect will also take into account how their donations funge with OP).
Thanks!