Sorry, you're right. I had checked that it went in the Agnes socket, but in my original post I typed the wrong socket name.
Looking at a pic of the A500 motherboard, it seems there's lots of room then between the Denise socket (Indvision) and Agnes (MegaChip).
Hopefully, there's not a hardware clash. I'm guessing not, but perhaps someone has these two bits of hardware installed?
As an aside - other than being able to use modern monitors with the A500, just how useful is the Indvision ECS on a stock 68000 machine with 2MB or less of RAM? Is it worth it?
Does a 68000 have enough horsepower to handle some of the higher-res new screenmodes the Indvision ECS offers?
If not then it might just be better to use a 1084 monitor (which I already have).