Programatically setting dropdown options in a matrix
I figured it out! Field-specific options need to go inside 'typesettings'.
'typesettings' =&gt; [
    'options' =&gt; [
        ['label' =&gt; 'H1', 'value' =&gt; 'h1', 'default' =&gt; 1],
        ['label' =&gt; 'H2', 'value' =&gt; 'h2', 'default' =&gt; ''],
        ['label' =&gt; 'H3', 'value' =&gt; 'h3', 'default' =&gt; '']
    ]
]