This was fascinating to me, as my expectation would be the trend should go in the opposite direction – i.e. *increasing* damage per CR for monsters intended to challenge high-level characters.

Hey, you know, I just realized I never really posted my results concerning your OP. So, here's how it works out and the assumptions made:

**CR 0 is not included**, as you cannot divide a number by 0.

**Tiers and CR:**
- 0 (CR 0-0.5)
- 1 (CR 1-4)
- 2 (CR 5-10)
- 3 (CR 11-16)
- 4 (CR 17-20)
- Alpha (CR 21+)

**Average PC Armor Class by Tier:**
- AC 15: tiers 0 and 1
- AC 16: tier 2
- AC 17: tier 3
- AC 18: tier 4
- AC 19: tier A (alpha)

Using the Attack Bonus by CR listed on the Monster Statistics by Challenge Rating table (DMG p. 274), I calculated the probability of successful attacks given the Average PC Armor Class by Tier and its impact on average Damage/Round to weight the effective Damage/Round. Since this calculation involves an Attack Roll analysis, I've included the adjusted damage for rolling a critical hit as well, which has been factored into the effective Damage/Round.

Dividing the (effective) Damage/Round by the Challenge Rating, and calculating the average across the range of the tiers, we have:

**Tier 0:** 8.80 eDPR per CR vs. AC 15 (45.0% average hit probability)

**Tier 1:** 4.78 eDPR per CR vs. AC 15 (48.7% average hit probability)

**Tier 2:** 4.25 eDPR per CR vs. AC 16 (57.5% average hit probability)

**Tier 3:** 4.23 eDPR per CR vs. AC 17 (60.8% average hit probability)

**Tier 4:** 4.47 eDPR per CR vs. AC 18 (65.0% average hit probability)

**Tier A:** 6.85 eDPR per CR vs. AC 19 (71.0% average hit probability)

As you can see, from tier 1 to tier 4, the effective DPR against average AC remains within a range of 4.23 to 4.78 per CR. While not exactly very narrow proportionally, it is fairly consistent.

An interesting observation IMO is that despite average PC Armor Class increasing by tier, the average hit probability across the tier

*also* increases! It it remained relatively constant, we could say that creature attacks "keep pace" with average PC Armor Class. However, it increases more than PC armor class to keep the effective DPR close.

The jump in eDPR in Tier A is due to the increased average hit probability, but moreso because we see increases in the maximum damage/round of 18 in most of this range, instead of just the 6 points we see in tiers 1-4 (excluding CR 20, since it is the first 18-point increase). Frankly, I'm a bit surprised it isn't even higher.