I already posted what I think you should be doing.
btw - I think you’ll find search engine bots are wide awake to the very obvious way you are trying to “sneak” keywords into supposedly higher relevance elements.
<div class="text">This is my <h1>Keyword</h1> I am using!</div>
I used a <div> instead of a <span> otherwise it won’t validate. But why not use it the other way around If I may ask. Use a heading and use <span> inside of your heading to create size differences, if that’s where you’re after.
Why are you adding h1 in the middle of a sentence? What are you trying to achieve? I’m sure there’s a better way of doing whatever it is you want to do.