My reference point is 4 SP per pair, which is effectively the original 2 SP per share you mentioned. However, I got confused on the procedure of what happens with the 1 STEEM when there are new sign-ups into pool #2, so thanks for clearing that up.

If the end result is that the 2 SP per share delegated to pool #2 comes from a lease, and then when the lease expires so does the delegation (thereby requiring pool #2 to rely on its own earnings plus its 25% share from pool #1 from that point forward), then the whole system makes sense. I hope that I've correctly understood how the waterfall works now.