I did some testing.
Harder/later maps can start on higher Wave numbers when a Character's Level is 'high for the map'. More so on later/harder maps, but earlier maps limit this, to as little as "starting Wave +1", or maybe even +0. Plus, in theory, if someone has a Lvl 20 CHAR they could switch to, but they and everyone else are playing with, say Lvl 3 CHARs, the starting wave would still be increased, because one can switch to any CHAR over the course of the map.
An xBox Live account with just one Lvl 1 CHAR and no other CHARs would always start with 'Wave 1' when playing 'solo'.
EXAMPLES:
When we first started playing this game,
BOTH My Wife and ME, one Lvl 1-3
CHAR each, "Foundries and Forges" on MEDIUM: Wave 1
(I wanted to start over anyway, so tonight i deleted all my CHARS for testing)
Now,
JUST Me: 1 CHAR, Lvl 0, "Foundries and Forges" on MEDIUM: Wave 1
WITH My wife: 1 CHAR, Lvl 16, "Foundries and Forges" on MEDIUM: Wave 2
JUST My wife: 1 CHAR, Lvl 16, "Foundries and Forges" on MEDIUM: Wave 2
WITH Me: 1 CHAR, Lvl 0, 'quarters on MEDIUM: still Wave 2
JUST My wife: 1 CHAR, Lvl 16, "apprentice's quarters" on MEDIUM: Wave 3
WITH Me: 1 CHAR, Lvl 0, "Apprentices's Quarters" on MEDIUM: still Wave 3
Including a lower Exp CHAR in a multi-player game full of high-level CHARS MAY lower the starting wave,as asserted in a different answer -at least on some maps- but I don't know.
There are countless other factors that may be included, but the 'difficulty' of a map seems to cap the adjustment, early maps most of all.
Complicated stuff, lets get some data!
Can anyone provide empirical data to disprove this line of thinking?
Include number of players, number of each player's CHARs, and the range of their CHAR's EXP, the map and difficulty, and the starting wave.
Best Answer
From the multiple times my friends and I have run this level 20+ (we've been farming it for mana and a better version of the weapon he gives). He has always spawned from that side.