OK, so a bit of a caveat with these Zacasi (or ZACASi) seat covers, more to do with customer service than product quality. They replied the opening in the side of the driver's seat cover is for "level for vertebra", which I believe is a poor translation for lumbar adjustment. It did not appear on the menu but was automatically inserted in my order by their online configurator.
Their mistake, they should fix, right? Apparently not. They say I should have picked it up when I reviewed the order specs before confirming, so they don't feel responsible. Can't say I agree so I've appealed and hope to hear better news soon.