Concerning spawns, it's important to know that ALL ATTACKERS spawn at spawnpoint 32 at the beginning of the round (like in battle mode). Another important thing is to also calculate enough space around the rest of the spawnpoints (don't place them directly in corners, etc.), since sometimes multiple ppl are spawning at one spawnpoint, pushing each other away (and sometimes off a wall or cliff, if the spawnpoint is too close). This happens before the players can actually react, and it can look as if they had spawned in free fall.
Also, it can't be repeated enough times: siege spawnpoints ARE NOT ORDERED. It's not guaranteed that defenders spawn at 0-31 and attackers at 32-63, as a complicated distance and hostility system determines spawn locations. You can easily verify this by placing spawnpoint 2 or so close to 32, and it will be used for attackers and never for defenders, because spawnpoint 32 is used as the location for "attacker base". What I'm not sure about is whether the flag or spawnpoint 0 counts as "defender base".