On the "IRA Information Worksheet," I am prompted to enter the combined value of all traditional IRA on line 18.

Is this figure simply the FMV of the IRA based on the 5498?

When I enter these figures and also enter a non-deductible IRA contribution, it decreases the non-taxable portion of the IRA Distributions on Form 8606. If I do not enter these figures, the non-taxable portion of the IRA distribution increases significantly.