User blog:Uncommon22/Do elements matter when leveling BB?

I know that you use the same type of BB (offense, buffs and healing types) in fusion to level the BB but does the element of the UNITS matter? For example, can you level the BB of a fire unit by fusing with a light, dark, water, earth or thunder unit of the same BB type? I've tried a bunch of times with no success and I feel like I'm wasting time, money and units... Oh and for offense ones does it matter if they target a single or all enemies?