Not sure what your Mount is, but for the dovetail to be longer than the clamshell is a waste. Technically it only needs to be long enough to fill the Mount aperture but that may not allow optimum mechanical connection between the dovetail and clamshell becoming a point for flexure. Also, a dovetail bar approaching the length of the clamshell will allow finer tuning of the alignment of scope axis and Mount axis.
In reality, a compromise.
How long is the saddle? Some saddles clamp better if the dovetail bar is at least as long as the saddle. A longer bar also allows you to balance the load by sliding the dovetail in the saddle rather than loosening the clamshell clamp and thus risking marring the OTA should there be any grit on the OTA .......
I always use a dovetail that is at least as long as the saddle...
Its nice to have some extra length for future options. You might put a piggy back scope on that changes the centre of gravity, or want to hang a utilities box somewhere.
Otherwise, being able to move enough to accommodate COG is the important thing.
