user bucket size

When I make a render region to tune a material I need very small bucket size :sometimes I need to render region with print resolution so my bucket size is 150*150 (an average,take them as an example ) with the tiny bucket dimension from solid rock panel and if my render region is 600*600 I can't use all my cpu's, I need 40*40 bucket to use all of them .If i change the bucket size in the Vray setting and I hit the render bottom from SR panel the bucket size change to SR option.The only way to use vray setting is to render from Vray panel ,is it correct ? Can you add a "user bucket size" in the Sr config panel (a wish )

Bye
Gianmarco

Hello. And Bye.