Did some testing, forgot to add in map sizes but that will come at a later time.
Well since solo map testing, the following is based on:
... 0 EPs mod on map & events
... 0 XP gain on map & Events since this will alter results
...
0 +% Swarm on map mod = WORSE map mod to ruin levels.
... NOTE: All tests done with easy mode DISABLED, so this should be pretty close.
Map Level 10 (Mlvl 35) ... You roughly gain 5 levels... so you can start @ level 30.
Map Level 25 (Mlvl 50) ... You roughly gain 15 levels... so you can start @ level 35.
Map Level 40 (Mlvl 65) ... You roughly gain 20 levels... so you can start @ level 45.
Map Level 45 (Mlvl 70) ... You roughly gain 25 levels... so you can start @ level 45.
Completed the level 45 Map starting @ level 46.81% to 70.05%, Volcanic Map, so Frisps are annoying as in % chance to call another one.
I will put in some other level maps later on, but I can see a good pattern there... so 1 level 25 Map to level 50, then start a level 50 map to 75...
https://prnt.sc/11p0ut031 across by 20 down. = 620 squares