ionic content with scroll

I have a view in ionic which has an image at the top and a scrollable list of messages. I want the image to stay on the screen while the list can be scrolled. Here is my current code:

<ion-content scroll="false">
    <img src="/myimage.png">

    <ion-scroll direction="y" style="height: auto;" delegate-handle="postScroll">
        <div class="list">
        <a class="item item-avatar" ng-repeat="post in posts">
          <img ng-src="myimage.png">
          <h2>{{post.title}}</h2>
          <p>{{post.content}}</p>
        </a>
        </div>
    </ion-scroll>
    </ion-content>

This works pretty well, i.e. the scroll does work and the image stays in place. But I am having trouble setting the height. If I have 100 posts, for example, I can only see 2-3 since the height container is not nearly large enough. Am I doing this correctly? How can I set a variable height for the number of posts? The user can add posts dynamically so this height needs to be able to change.