Maphyr shirt only affects an item with a "grade" such as D, C, B, A, S, S80, R, R95, R99, R110.
When enchanting items without a grade, use dragon shirt.
There isn't a set correct number of luc which will all of a sudden allow you to enchant easily. Luc's primary point is to enhance the lady luc proc chance, and to evade killing blows.
On this cloak event, Ncsoft still refuses to put the stable 11-15 scrolls in the store again for hero coin, so I don't think you will see many 10-15 cloaks again unfortunately. You have to have a means to remake 15 easily to try for 18+