How do I control the Layers to be obstruceted in LEF ??

[kirangu]

Hi,

I am writing out lef from SoC encounter and by default too is placing all layer obstruction all over the block.
When I read same lef in top level blockage is visible all over the block.
How do I control it till the particular layer and particular portion.

For ex: If I have block of 500 x 200
I am creating blockage in 300x200 area.
Lef OBS LAYER M7 is showing 0.00 0.00 500.00 200.00

I want OBS only in 300x200 area. How do I do it?? Please help.
Also If need ons only till M6 layer it should not obstruct layers above M6. How do I do that ??

Thanks,
Kiran