TOPN in Calculated Column

Aim:
I need to generate a calculated column that show the SUM of the last 6 results by person. 

Context:
Ordinarily do this as a measure, however, due to needing to put the result ( % Diff of Most Recent to Avg of Last 6) in a box and whisker plot it has to be as a calculated column. 

Intended Outcome:

Data Structure:

• The relationship between the two tables is on the FT_PlayerID. 
• The Box & Whisker CMJ Table has been calculated as a summary table with the following DAX: 

Box & Whisker CMJ = 
SUMMARIZE(
    'CMJ Results',
    'CMJ Results'[PlayerName],
    Players[FT_PlayerId],
    "Most Recent CMJ", CALCULATE(MAX('CMJ Results'[Max Height]),LASTDATE('CMJ Results'[SessionDate])),
    "Most Recent Session",MAX('CMJ Results'[SessionDate])
)

• The player Index Number in the CMJ results table assigns a sub index so each player's test has an index number - this is so I can calulcate the TOPN off.
  
  

Many thanks in advance!