 chain state
has shape <code>[C0, C1, Y]</code> (meaning that there are <code>C0 * C1</code> total chains) and
<code>log_accept_prob</code> has shape <code>[C0, C1]</code> (one acceptance probability per chain),
then depending on the shape of the step size, the following will happen:</p><ul>
<li><p>Step size has shape <code>[]</code>, <code>[S]</code> or <code>[1]</code>, the <code>log_accept_prob</code> will be averaged
across its <code>C0</code> and <code>C1</code> dimensions. This means that you will lea