Here are options to help optimize chances for generating preferred Monuments on the RustMaps.com custom procedural map generator.
Trainyard: Will only spawn under size 4250 if set to Try Generate and Generate Above Ground Train Tracks are also set to Try Generate.
Launch Site: Will only spawn below 3500 if set to Try Generate.
Excavator: Will only spawn below 3500 if set to Try Generate.
On the Map Gallery filter:
Use the Large/Small Monument filters to select the Monuments you prefer.
Adjust the Map Size filter till you see an appropriate size for your needs.
On the Map Gallery filter:
Adjust the Map Size slider to select the World Size to be generated.
Increase the Monuments minimum filter to reduce the number of seeds listed.
Adjust the reduced set of map seeds for custom map generation.
Use Optimal Size.
Use Optimal Seeds.
Enable Change spawn rules.
Changing the monument spawn rules increases the chance of generating preferred monuments. However you might find a high tier monument next to a player spawn beach.
Try Generating Maps.
If you're still not seeing the monuments you prefer try:
Enable Custom island intensity and set to 0
The lower the intensity, the lower the number of islands that will be generated. This also increases the main island size. 0 = one larger island, 5 = normalish, 10 = more islands.
If this is successful, try regenerating the map with a higher island intensity number (1, then 2, then 3, etc), for a more normal terrain.
If island intensity 0 is unsuccessful, try increasing the world size by 50 or 100 and finding a new optimal seed.