Great that more people are starting to use the foil wrap.
@Moridin you have not mentioned what species this is. Looks like some sort of maple which are great for ROR but I would be a little wary of having soil over the top of the foil. Tridents in particular are prone to throwing new roots at surface level. If one escapes over the top of the foil it will usually grow faster and thicker than any others and destroy all the good planning and work. I would just brush the soil away from the base of the trunk until the foil is exposed to prevent wayward roots escaping over summer.