Thanks for posting here in the Community, @wn1.
Let's go over to your FSA payroll item setup so it will be deducted from wages before calculating pension deduction. However, I'd still suggest consulting your Health Insurance administrator to determine the appropriate tax tracking type of this item.
If taxable is selected, this means that wages or contribution items are fully taxed. Deduction items are exempt from tax and reduce taxable wages if Pre-tax is selected.
Once you've verified from your insurance provider, you can review your payroll setup and make any changes. Here's how:
You can also check out this PDF article for more details about the Health Savings Accounts and other Tax-Flavored Health Plans: IRS Publication 969. In case you want to learn more about the benefit plans and their limits, please see this article: Benefit Plan Contribution Limits for 2019.
This will get you in the right direction, @wn1.
I'm here anytime you have other payroll concerns. Have an awesome day.