I would also be concerned. Sounds like my cycle that I converted to an IUI. If my follicles get very big, even over 20, they don't fertilize. It sounds like maybe they are thinking about sacrificing the larger follicle for the smaller ones. If they just go after the larger follicle, it sounds like you will only get one.
Are you self pay? Is that why you don't want to convert? I hate converting, and until recently all my meds were out of pocket (everything else still is), so I understand going forward if that is the case. But, if your meds aren't out of pocket, I would convert and try again. It sounds like you have follicles. They just need to try another protocol to somehow suppress the dominant and get the other ones together. I know it seems impossible to do, especially when we all have tried so many protocols, but there are still many more than can be attempted.