Are slurs-on-ties like buses? You wait for ages, then several come along at once? This question has come up several times in recent days, or am I simply unknowingly stuck awaiting the arrival of an underground rodent?
Slurs can’t start and end on the same note, so when a note is tied into a chord in the same voice, at least part of that phrase is one note “event”. A more reliable method could be to put the upbeat into another voice, force the tie by selecting the start and end notes before tie-ing? If memory serves that should make the slur more reliable.