Section 179 Expense Deduction

I was considering purchasing a "new" (used vehicle) for business and potentially personal use, before the end of the year to try to take advantage of the section 179 deduction.  However, when I enter a December date, the actual expenses method deduction, i.e. that allows me to choose this option is negligible.  I noticed if I enter an in earlier placed in service date the deduction is considerably more.  For example difference between a first of the year date and a December date is in my case almost $8k.  So, it seems it's in one's interest to buy a vehicle as close to the beginning of the year as possible to maximize this deduction.  Is it that simple or are there other nuances I may be missing?  I am self-employed, i.e. the vast majority of my income is Schedule C business income.   To what degree does the business vs personal use affect the total available deduction?