Thanks guys, this will also let me use my non-standard park position of the scope in the horizontal position 
I've amended these options (center was already ticked) on my saved sequences so I'll give it a try the next time the clouds move on.
One other thing, do you recommend using the default exposure settings for the plate solve image? AstroTortilla was previously set to ISO800 & 10sec but if the default 256k & 1sec work well then that makes life simpler I guess.
Pete