Floorplanning issues

 Hi,

i am working on floorplanning and i have specified teh width & height in DIE size option. i saw the layout and die and core boundaries are perfectly aligned with each other as shown in fig1.

when i gave the core margins by (i tried both ways) with equal distance then (10.0 10.0 10.0 10.0) and then in layout. the die and core boundaries are not the equal distance which i have provided as shown in fig2 (differnece is 10.8 10.8 10.0 10.0).

is there anything wrong any specifying the co ordinates??

i tried with other way also like with aspect ratio ( i have taken aspect ration, upto 10 digit after decimal) and checked but here my W & H are changing which i dont want. size should be correct.

by abole method i am loosing some die area when i am creating the core power power ring width because power rings are palceing with die core as boundary, so iam wasting nearly 3u of one cell row.(my height is mulple of cell row hieght)

what will be the cause for this

why die & core boundarie are not aligned to each other?? 

please suggest.

Regards,

Kul