Everything you describe is counted correctly, apart from the fact that you may have done a level 1 delve and forgot about it. EDIT: The rewards track counts “delves and world activities”, so you might have done a “world activity” that the game counts as a level 1 delve.
I’ve answered this question in another thread where you can check the screenshot in the OP to see that delves need
- 2 completions for the first reward
- 4 completions for the second reward
- 8 completions for the third reward
The TL;DR version: every delve reward tier looks at your completed delves in the week, going down a list from your highest to lowest completion, and always takes the lower level complete of the tier to calculate your reward.
Long and elaborated version:
When you check the delve tiers in the great vault, you will see that the first two tiers are two delves completed each (not one as it used to be with the first tier of dungeons, which is where the confusion might stem from).
Out of those delves completed, the reward tier always counts the lowest one.
So if you complete 3 delves at 6, 5 and 5, your first delve reward tier in the great vault will be level 5 (highest 2 delves is level 6 and level 5 → level 5 reward).
You should not be getting a second tier reward (4 delves completed) at all, unless you’ve actually completed 4 delves.
Let’s assume you completed a level 6, two level 5 and a level 1 delve.
That means:
First delve tier: Level 6 + first Level 5, lowest counts → Level 5 reward
Second delve tier: second Level 5 + Level 1, lowest counts → Level 1 reward
If you did only 3 delves, then the second tier should offer no reward (minimum delves completed not met).
To get a level 6 reward in the first tier, you need to complete 2 delves at level 6.
To further elaborate:
Assume you did the following delves in a week.
Level 8
Level 8
Level 6
Level 5
Level 3
Level 1
Your first delve tier (complete 2 delves) is a level 8 reward, because you completed 2 delves at Level 8.
The second tier (complete 4 delves) is a level 5 reward, because you completed a delve at level 6 and one at level 5.
If you continue completing delves at, say, level 7, to make the list look like this:
Level 8
Level 8
Level 7
Level 7
(…)
Your first tier will be a Level 8 reward, the second tier will be a Level 7 reward.
If you then go further:
Level 8
Level 8
Level 8
Level 8
Level 7
Level 7
(…)
Your first and second tier delve rewards in the great vault will be Level 8.