In Engraving Options there is a setting for ‘Minimum horizontal span for glissando lines from grace notes’. In Dorico 220.127.116.112 this setting has no effect no matter how large a number you enter—unlike the ‘Minimum horizontal span for glissando lines’ (i.e. between ordinary notes), which works as expected.
Thanks for reporting this, Kim. It turns out that due to a little bug in the processor that uses this value, this value only takes effect at the very start of the flow. I will make sure this gets fixed.