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You're mixing a rule for what can be deducted under IRC 263(a) and section 179.

The safe harbor for small taxpayers is for what can be expensed for the year for repairs , maintenace. and improvements when you meet the qualifications. Thus if the expenses qualify, section179 never enters the picture 

for 179  qualified improvement property 

Qualified improvement property. Generally, this is
any improvement to an interior portion of a building that is
nonresidential real property if the improvement is placed
in service after the date the building was first placed in
service.
Also, qualified improvement property does not include
the cost of any improvement attributable to the following.
• The enlargement of the building.
• Any elevator or escalator.
• The internal structural framework of the building.

 special/bonus deprecation has different rules but this too does not apply to anything expensed under the small taxpayer election, then 179 if any is applied then the remaining cost of up to 80% can be expensed for qualified property

Certain Qualified Property Acquired
After September 27, 2017
You can elect to take a 80% special depreciation allowance for qualified property acquired after September 27, 2017, and place in service in 2023,  Your property is qualified
property if it meets the following.
• Tangible property depreciated under MACRS with a
recovery period of 20 years or less.
• Computer software defined in and depreciated under
section 167(f)(1) of the Internal Revenue Code.

Qualified property acquired after September 27, 2017,
does not include any of the following. See PUB 946 starting with page 24

https://www.irs.gov/pub/irs-pdf/p946.pdf 
• Property placed in service, or planted or grafted, and
disposed of in the same tax year.
• Property converted from business use to personal use
in the same tax year acquired. Property converted
from personal use to business use in the same or later
tax year may be qualified property.
• Property required to be depreciated under the Alternative Depreciation System (ADS). This includes listed
property used 50% or less in a qualified business use.
For other property required to be depreciated using
ADS, see Required use of ADS under Which Depreciation System (GDS or ADS) Applies? in chapter 4.
• Property for which you elected not to claim any special
depreciation allowance 
• Property described in section 168(k)(9)(A) and placed
in service in any tax year beginning after December
31, 2017.
• Property described in section 168(k)(9)(B) and placed
in service in any tax year beginning after December
31, 2017.