https://sagy.vikingove.cz/en/defining-slavic-shields-of-9th-11th-century/
Found during my research into Rus shields and if mentioned elsewhere apologies for duplication but this is a really really good article. Its absolutely fascinating and worth reading. I did chuckle at the end when the author discusses why bossless shields aren't used much by reenacters and it's very true....
We did mention this in the earlier discussion of Rus shields
http://soa.org.uk/sm/index.php?topic=5817.0
The Project Forlog website/blog has been mentioned before. Well worth a look in general if you are interested in Early Medieval warfare.
Ah indeed, apologies for the doubling up. Really good info