You'll have to excuse the "C" I used in the "-dmC" I tried suggesting another feature but it seems it could already be done when setting x and y pos as both -1.
But what I thought is again just like the /window command -C should center the dialog when being opened. But I think we should have that option if your x and y positions are 1 and 1. So not only will it open at the respected position but mIRC will ignore it if C is in your switches.
I like your clientedge and staticedge ideas, very snazzy.
-Andy