killed 106 +1
They did taranto or the planes cannot return +2
you killed both their fleets and the only ship left they have is a dd and or ca +2
they bought fewer than 6 infantry +1
they bought fewer than 4 pieces on london +2
you stratbombed them and were successful (15+ damage) +1
if you do not scale at least 5 on this matrix I would decline the SL. I scored a 7 and was still at risk of losing UK the entire rest of the game.
Buying ships telegraphs the sea lion. save your money instead. Buy the entire stack as a surprise on the second turn and only if thing are favorable.