Sending the same proposal to multiple funding agencies I am planning to submit a proposal for possible funding. There are three sources of funding I can apply for, and unfortunately the evaluation periods all three overlap. Typically there exists an option to state this while submitting. I am wondering if such a statement has any impact on the chances of being funded (of the three grants, I much prefer a specific one). Moreover, two of the agencies uses external reviewers and since my proposed work builds heavily on the previous efforts of three persons (one of them a prolific reviewer), there is a risk in reviewer overlap. I wonder how a reviewer would perceive this. In particular, would a reviewer be less inclined to recommend a second proposal for funding if they have already recommended a first on the same topic? PS I was advised not to make any statement of overlap. Is this an  unofficial custom?
It really is better to not do it. At least simultaneously (might be ok if the proposal was rejected).
If you absolutely have to go ahead, try to fine-tune and change the proposal as much as possible according to the agency requirements.