At the start of some Foundry missions, I've seen not just a single box worth of dialogue which you choose to accept, but a full dialogue multiple layers deep that takes place before even reaching the door from your first Cryptic map into your custom-designed maps. This often takes place before your ship leaves whatever random system it happened to be parked in when you accepted the mission.
How is this accomplished? The Foundry doesn't seem to allow you to access the Advanced Dialogue Editor on that Mission Start box. My attempts to put a popup dialogue box before the first Cryptic Map didn't work either; the dialogue instead ended up upon arrival to that map. I'm sure there's something stupid I'm missing, but I still have to ask.
Also...is it a practice you recommend, or is it better to leave a longer exchange until the player has really started the mission in earnest?
No, you're not missing it. (Although I think this is a better thread for foundry discussion than missions. Don't worry, a forum mod may move it for you.)
If I recall, you do it by a method you tried, placing a story dialog pop up as the first option before any objectives. This may only be possible before you've added any maps, or, could be something only older missions can do if the mechanics changed with creating a mission with one of the season updates.
I've only used it a few times myself, so, someone may know more than me.
As for why I've only used a few times, it's personal preference for me. I think it's more apt for players to not get into a mission until they are actively able to take part, which, only for sure happens when they are at or near the door that starts the mission. It also helps in case they pick up a mission to play it later, and don't forget what text popped up right away. However, if the only other option for you is to send them to say ESD for a briefing before sending them back out to another planet 2 or 3 sector blocks away... do it with a story pop up right after mission accept.
I tried doing a popup dialogue both before and after adding a map. Before adding a map, the button was greyed out. After adding a map, it simply refused to let me slide the popup in between and placed it automatically onto the next map.
My Foundry creation attempts have only been during Seasons 6 and 7. Maybe a liiiiiitttttle bit during Season 5, but not much.
(BTW, yeah, I realized I'd posted in the wrong forum as soon as I did it. I hope a mod will fix this.)