M9K Block RAM calculation

Hi All advanced:

i use EP3C16Q240C8 FPGA,and created some Block RAM in my design,

but Quartus tool report M9K utilization is very strange.

Block RAM describe as below:

1.Single Port RAM,width = 144 , Depth = 512 , Size = 73728bits ,

73728/(9X1024) = 8 , compilation and report total use eight M9K , it is reasonable

2.Single Port RAM,width = 144 , Depth = 64 , Size = 9126bits ,

9216/(9X1024) = 1 , but compilation and report total use four M9K , it is unreasonable

so how to calculate M9K Block RAM ?

Ex:9216bits = ? M9k