Understanding the factors influencing successful engagement with Embodied Conversational Agents (ECAs) remains a significant challenge. This understanding could be used to personalise agents to users to improve interactions. Some studies have shown that simulating personalities in healthcare agents can improve effectiveness and engagement. However, it is not yet well understood how variations of agent personality can be leveraged to improve user engagement with Motivational Interviewing (MI) ECAs. Specifically how the balance between agent warmth and directness can be controlled in an MI agent to improve likeability and engagement. We conducted an online Wizard-of-Oz (WoZ) mediated study of two variants of a motivational ECA to investigate user perception and attitudes towards warmth and directness in interaction style. In our MI scenario, participants rated likeability and engagement higher for the direct agent variation. This effect was not as strong for younger participants or participants who were not native English speakers. This result gives us a direction to improve MI ECAs to make their increased adoption more likely.