I'll make sure to help you out on this, abdomunla.
Thank you for sharing screenshots and I also appreciate the steps you've performed. Let me provide additional details when importing a custom template in QuickBooks.
Yes, you have the option to map a template field. However, when you click on the drop-down in the QuickBooks Field column, there are indicators as to which part of the fields should that be when importing them in QBO. Let's say for example Total Tax, it should be in the invoice summary (Footer) part, not in the invoice line (Body) part.
I understand the need for having the tax amount to show in your invoice, so I'm personally taking note of this suggestion and send it to our developers. This helps them in deciding on what features might be added in their future product updates.
Be sure to get back to me if there's anything else you need. I'd be happy to help you all the way.