When I have mIRC minimized, it appears on the upper left corner.
When I maximize mIRC, it appears near the center of the screen, at the center of mIRC.
When I have mIRC open, and have it as a 600x800 square at the bottom left corner, it appears in the center of the 600x800 mIRC box at the bottom left corner.
It appears at the center of the main mIRC window, however if the main mIRC window is minimized, it calculates the mIRC window as being 1,1 on the screen, and fits the dialog box in.
Those who can, cannot. Those who cannot, can.