If you haven't already, check with the Edmunds forum on Niro leases:
https://forums.edmunds.com/discussion/49215/kia/niro/2018-kia-niro-lease-deals-and-prices/p4
You can ask the moderator for the current money factors, and residuals, and then plug your numbers into a lease calculator to get monthly payments. Don't know if your figures above include sales tax or not.
I'm seeing currently residual is somewhere around 53% of MSRP for a 3yr/12K lease. A 15K will be a little lower. It looks like the money factor is around 0.0022 (5.28%). There is $3000 Kia lease cash, I believe. Your monthly lease will depend on your capitalized cost, which is essentially all your upfront costs (vehicle price, additional dealer costs, lease acquisition fee, etc, factoring in the $3000 lease cash).
The current Niro money factor is pretty high, and the residual is pretty low, so you're going to have a tough time going below $400/month. The interest charges alone are more than $80/month. Taxes at 7% are about $20/month.
I leased my 2017 LX with adv tech package for $330/month, sign and drive, including all taxes, no money down. The EX premium is $6K more than this, so you would be leasing 47% of this or so, around $2800 more than mine. This will add about $80/month just for the principle, plus the extra interest and tax.
If your capitalized cost is $30,000 (with no sales taxes), for example, my lease calculator says $486/month including monthly sales tax. For a 12K mile lease.
If your cost is $29,000(with no sales taxes), it goes to $454/month, including monthly sales tax.
$433 doesn't look too bad, especially if it includes sales tax.
Caveats apply. I don't have access to the exact lease terms. Check the Edmunds forum above. Sometimes these are different for each state.