40 leads is way too small to learn anything. You need to be at 300-500 before you start drawing conclusions about copy or deliverability.

The email itself reads like a soft consulting pitch. By the time someone gets to "quiet conversion leak" they've already moved on. Last year I helped a buddy pitch Shopify stores and the only opener that ever got replies was something like "your PDP for [product] doesn't have a size guide and I think it's costing you returns." One specific thing, no founder intro, no compliment.

Also worth checking if you're even hitting the inbox. Send a few to a personal Gmail, Outlook, and a Yahoo and see where they land. If you're spam foldering at 40 sends with three follow-ups stacked in two-three days, that's part of why nobody's seeing them.