Depreciation Calculation

Hello,

i use JDE 9.1.5 and i have the below issue:

i have an asset with cost 6000 for 12 month start in July 2016 i used the below  rule and formula

and the formula as below where 999 =(10/3)*6   :::   10 basis amount and         03 Asset Life in Periods and         06 Asset Life Periods in Current

the monthly depreciation is 500 from July to December 2016 with total of 3000.

now i need to extend asset life from 12 month to be 24 month starting from January 2017 this mean i have remaining 18 month and remaining depreciation 3000  which should be 3000/18= 166.66 monthly until it finish in 2018 the issue i have that when i changed the life month to 24 the monthly deprecation will consider only this year 2017 this mean the system divided the remaining 3000 over 12 month of the years 2017 and the fully depreciated by DEC 2017 however asset still have 6 month in 2018.