That's just how the Survival event and Survival conductor work. The idea is to spawn enemies around the player to try and overwhelm them. If you want it to spawn on a marker, or even in a connecting module, you'd have to hand make your event which I would argue is probably better since you can tailor it more to your wishes.
Insert trigger action > start timer > Timer > On Timer end > Stop Repeater
Above Trigger action > Signal Repeater > Repeater (With an appropriate delay of your choice) > Signal > Start encounter > Custom Encounter
You could lengthen it and even use a random relay with additional Custom encounters to make the event more varied. Custom Encounter has options for spawning near the node or in connecting modules in addition to spawning on the player, so go nuts with the encounter, seriously this is how you make something cool!