Question about Horus Heresy novels timeline.

Just a quick question, I’m planning on reading the HH series in chronological order from start to finish. A massive undertaking but something to work at (and enjoy of course). I’m nearly finished Horus Rising and have the next 3 on my kindle ready to go.

The Siege on Terra volumes… are they meant to be read AFTER the original HH series, or intermittently?

I’m just curious and thinking ahead despite being a LONG ways from that point.

Thanks!