Yes, I grabbed IRD amount instead of the actual estate tax of 381,000, so you would still receive your total deduction by the time the IRA was drained the way you have been doing it. However, you could have deducted the estate tax at a faster rate by using the Pub 559 formula and the 2019 deduction would be nearly 100,000 using that formula.
Since the method you have been using has never been questioned, you could be consistent and maintain that to the last year. If you report a drastically increased deduction for this year in proportion to your 1099R, it might trigger an inquiry. So could any amended returns you file for 2016-2018. However, now that it appears you would complete your deduction in about 3 years without losing any of the total deduction of 381,000, it may be better to stick with the method you have been using which still generates the correct total deduction, just at a much slower annual rate than you could have received it by using the Pub 559 formula.