I don't understand your chart--it doesn't seem to be measuring what I would expect it to measure. For example, at first level, if #Easy is supposed to be the number of Easy encounters a four-man party can fit in a day, it should be 8, not 12. (Easy encounter is from 100-199 XP, so 150 on average, and you can fit in eight of those in a 1200 XP budget day.) Each PC will beat 300 XP worth of difficulty that day, which means they might level up in a single day--the only reason they wouldn't would be if much of that difficulty came from "adjusted" XP. So E Days should likewise be 1, not 1.7.
Yeah, I probably should have described the chart a bit better. Sorry about that. First of all, there is a sheet for backend data that has the core CR chart and a place for group size:
On the main sheet, I'll go over the fields and explain any calculations I made.
Level and XP
Should be self-explanatory.
To Level
Simply a calculation of the current level xp subtracted from the next level xp, to get a total xp value needed by *each* character to level up.
Easy, Medium, Hard, Deadly
These fields are simply extrapolations of the CR Encounter Building chart and party size., using the rules in the DMG. For example, it shows that a medium difficulty (at its lowest xp) encounter for a party of 4 level 1 characters would be 200 xp (50x4=200). A hard encounter would be 300 xp ( 75x4=300).
#Easy, #Med, #Hard, #Deadly
These fields are the number of each encounter type it takes to level up. This is not the same as the number of encounters that happen in a day (or per long rest). At it's most basic, you can consider this a calculation that divides the xp needed to level by the relevant encounter xp value. For example, a group of 4 level 1 characters needs 1,200 xp to level up. An "easy" encounter is 100 xp, which means it takes 12 such encounters to reach the needed 1,200 xp to level. I think where you're differing from me here is that you're trying to average out what an "easy" encounter's xp actually is. I handle averaging thing out later in the process.
E Days, M Days, H Days, D Days
These fields are pretty simple. Since the DMG referenced "6 to 8 medium or hard encounters" per day, I averaged the result to get 7. I then simply take the number of encounters required to level up, and divide by the number of encounters expected each day, to get a baseline. For example, since it takes 12 Easy encounters to level up the above example group, I do 12/7 for a total of 1.7 "adventuring days."
Sessions
Assuming each session equals an adventuring day, the goal of this field is to calculate how many sessions it takes to level. More importantly, this is where I run some averages and attempt to take into considering the differences between the base xp value of an easy/medium/hard/deadly encounter and the actual range (encounters aren't often balanced at the base level). To do this, I simply average the Medium, Hard, and Difficulty results from the previous fields, under the assumption that most encounters will fall in the middle of their encounter difficulties, with the occasional deadly boss fight. I specifically excluded Easy encounters from this calculation because almost no encounters seem to balance close to the bottom of that difficulty.
End result is this chart (linked again in case this post ends up on another page).
Without getting too obsessive over encounter building, I found the chart to be pretty accurate during the course of several AP's and custom campaigns I've run. It also helped me identify interesting quirks in the leveling chart. You'll notice it's separated into the 4 tiers of levels, and the speed at which you level is clearly changed for each one.