SSTB restrictions kick in at the threshold levels. If they are below the threshold levels the restrictions do not apply. Below taken from IS FAQ regarding section 199A & SSTB's.
8. In 2018, I will report taxable income under $315,000 and file married filing jointly. Do I have to determine if I am in an SSTB in order to take the deduction? Is there any limitation on my deduction?
A8. No, if your 2018 taxable income is below $315,000, if married filing jointly, or $157,500 for all other filing statuses, it doesn’t matter what type of business you are in. You will be able to deduct the lesser of:
a) Twenty percent (20%) of your QBI, plus 20 percent of your qualified REIT dividends and qualified PTP income, or
b) Twenty percent (20%) of your taxable income minus your net capital gains.