In spark, spark.driver.memoryOverhead is considered in calculating the total memory required for the driver. By default it is 0.10 of the driver-memory or minimum 384MB. In your case it will be 8GB * 0.1 = 9011MB ~= 9G
YARN allocates memory only in increments/multiples of yarn.scheduler.minimum-allocation-mb .
When yarn.scheduler.minimum-allocation-mb=4G, it can only allocate container sizes of 4G,8G,12G etc. So if something like 9G is requested it will round up to the next multiple and will allocate 12G of container size for the driver.
When yarn.scheduler.minimum-allocation-mb=1G, then container sizes of 8G, 9G, 10G are possible. The nearest rounded up size of 9G will be used in this case.