A break shorter than comma

I am trying to make the following sentence be said naturally by Amazon Polly (using Matthew neural voice) :

<speak>
<prosody rate="80%">
For each number i from 1 to n, we add i to the sum. 
<mark name="end"/>
</prosody>
</speak>

It needs a break after i, but not as large as a comma. I tried using <break time="0.1s"/>, but no matter how small a time I specify, the break is same as a comma. Is there a way I can cause a natural break after i?