The net earnings that remain after the solo 401(k) contributions is what is left to support the SE health insurance deduction, not the other way around. Also note that net earnings are net profit minus the deductible portion of SE taxes. In other words, net profit first goes to the deductible portion of SE taxes, then to your solo 401(k) contributions, then to your SE health insurance deduction. TurboTax does all of these calculations as described by the IRS.
The SE health insurance deduction is a personal deduction, not a business expense.
The one thing that TurboTax does not have the ability to do is to enforce the limit on employee elective deferrals when the individual also makes elective deferrals to another employers plan. In that case the Maximize function for a 401(k) contribution cannot be used and the limited elective deferral must be calculated and entered manually.
