I like the idea of a tiered proposal: "We hope to enroll X number of participants, because with that number, we can accomplish things A, B and C. However, if only Y participants are feasible (for reasons Q, Z, and W), we would be able to address these aspects of thing A and portions of C."
Another possibility would maybe to do the "We believe this project is feasible, because we already see X number of people fitting the requirements every week/month/quarter, and the requirements of this project would add Y time and Q other resources which we have done in similar form." (In other words, whatever other relevant data that demonstrates you have manpower, space, ability to track, an existing population you know is there, or whatever else they had questions about.)
no subject
I like the idea of a tiered proposal: "We hope to enroll X number of participants, because with that number, we can accomplish things A, B and C. However, if only Y participants are feasible (for reasons Q, Z, and W), we would be able to address these aspects of thing A and portions of C."
Another possibility would maybe to do the "We believe this project is feasible, because we already see X number of people fitting the requirements every week/month/quarter, and the requirements of this project would add Y time and Q other resources which we have done in similar form." (In other words, whatever other relevant data that demonstrates you have manpower, space, ability to track, an existing population you know is there, or whatever else they had questions about.)