Retirement contribution allocation for business

I created an individual 401k plan for my consulting service. TurboTax calculated the maximum amount allowed to this plan, and I use that amount for the contribution.

But later is shows the screen Retirement Contribution Allocation with the field Amount of Contribution Attributed To This Business. I do not have any other business. I noticed taht if I put the amount less than maximum in that field, TurboTax gives me a higher refund. What should I put there?

Thanks