Lets look at a few numbers to get a feel for this:
First, here is the total XP you need to have to get to the next level. So if your level 2, you need 30 total xp in your bucket to level 3 (which is a difference of 20 xp, since you started with 10 at first level.
Level | XP |
1 | 10 |
2 | 30 |
3 | 60 |
4 | 100 |
5 | 150 |
6 | 210 |
7 | 280 |
8 | 360 |
9 | 450 |
Versus Fresh Units
This is our basic whether we upgrade our units versus just make a new one fresh, lets see how far behind some of our baseline units with the -50% xp penalty.
Scenario 1: Level 2 unit upgrade vs fresh barracks unit.
XP 5 vs 15 - need 2 melee attacks (5 ranged) to catch up
Scenario 2: Level 3 unit upgrade vs fresh armory unit
XP: 15 vs 35 - need 4 melee attacks (10 ranged) to catch up
Scenario 3: Level 4 unit upgrade vs fresh military academy unit
XP: 30 vs 60 - need 6 melee attacks (15 ranged) to catch up
High Promotions: Upgrade vs Fresh Military Academy Unit
Scenario 1: Level 5 -> Upgrade -> Level 6 vs Level 4 Academy -> Level 6
100 XP -> 50 XP -> 150 XP (100 XP, 20 melee, 50 ranged)
vs
60 XP -> 150 XP (90 XP, 18 melee, 45 ranged)
Scenario 2: Level 6 -> Upgrade -> Level 7 vs Level 4 Academy -> Level 7
150 XP -> 75 XP -> 210 XP (135 XP, 27 melee, 68 ranged)
vs
60 XP -> 210 XP (150 XP, 30 melee, 75 ranged)
Scenario 3: Level 7 -> Upgrade -> Level 8 vs Level 4 Academy -> Level 8
210 XP -> 105 XP -> 280 XP (175 XP, 35 melee, 88 ranged)
vs
60 XP -> 280 XP (220 XP, 44 melee, 110 ranged)
Conclusions: So what this is showing is that right around the level 4-5 mark, your home grown promotions are going to stagnate a bit. Its actually more efficient XP wise to make new units than it is to home grow their XP. Pushing into level 6 its faster to keep pushing your existing units and upgrade them than replace them with new units....but it does show a marked difficulty in pushing into those high promotions. I would expect that level 6 units would be exceptionally rare in this model, as by the time you get just enough Xp to get to that level, you need to upgrade your units again.