This might be really obvious and I guess I’ll end up answering my own question but I’m still new to this so that makes me want to check my learning!
I assume the type of portafilter you use will impact the brew time for your espresso? I.e a bottomless v double spouted. Therefore you would need to grind differently and dial in for each, presumably less fine for the double spouted as the portafilter itself offers more resistance?
I’ve just made a double shot (I know it’s 8:30 at night!) and used the same grind as I usually use for my bottomless. I wanted to split the shot and save one for tomorrow (I won’t get chance to make one before we leave and old coffee > no coffee) so used my double spout and the shot was nearly twice as long as usual.