I personally think healers should heal around his area instead of a straight line / W shape / X shape / any shape by default. This’ll reduce the risks that other players in the party to go around all over the places instead of sticking to the healer, which would be difficult for the healer to aim it. Having a party where healer is the in the center position of the group makes healing a lot easier and predictable for the healer to do his job. However, I do agree that this set up has its cons as well as an AoE attack from boss would be an extremely high risk for the party that always stick together.
But yes, a feature where the healer can customize the positions of tiles would be really welcomed as it provides a lot of versatility and adaption to the environment, party set ups and overall strategy of the battle outcome as different pattern of tiles will provides different pros and cons, considering all the elements available on the battlefield. It should, however, comes with a cooldown or something as its restriction though,