Do chances of admission improve if applying for summer versus fall?

Yes, indeed- I just checked and didnt find anything about using BF at Agnes Scott, so either I misremembered or they stopped meeting BF amounts. They’re still generous with scholarships and test optional (stueebts without a score must send a paper and/or participate in an interview).
Students dont need a SAT score to get BF as long as they have the full diploma/requirements for Cambridge (AICE) or IB. A strong student who is a poor test taker could easily get the 24 for IB or the AICE requirements.