Inserting a Singular Column in a Matrix relating to the Column before it

Hello All,

I have a matrix visual showing student scores in various attributes, I've created a improvement column in my data which just shows the image URL of an up/down arrow depending on the score. I've only created one of these Improvement columns so far in order to test it however the issue I'm encountering is that the Improvement column is showing after the score for every attribute rather than just the one it it is realted to despite the fact it only displays the image for the appropriate attribute.

Image of my Matrix Visual (Student names blanked out):

The code I'm using for the improvement column is: 

Confidence KPI Term 1 = VAR a= IF('Link Teacher'[Attribute]="Confidence End of Week 12",MAXX(FILTER('Link Teacher','Link Teacher'[Identifier]=EARLIER('Link Teacher'[Identifier])&&'Link Teacher'[Attribute]="Confidence Start of Programme"),'Link Teacher'[Score]))
return if(ISBLANK(a),BLANK(),if('Link Teacher'[Score]<a,"https://skilldrive.custardcloud.co.uk/nextcloud/index.php/apps/gallery/s/K9MlM3qRppH2pIZ",IF('Link Teacher'[Score]=a,"https://skilldrive.custardcloud.co.uk/nextcloud/index.php/apps/gallery/s/UfuwdLzP8wKr8py","https://skilldrive.custardcloud.co.uk/nextcloud/index.php/apps/gallery/s/UO9mrv0CBmW1A8t")))

And finally my data looks like:

Student Name  Identifier  Attribute                                 Score  

xxxxxx                xxxxx       Confidence end of week 12           5

Any help greatly appreciated.

Many Thanks,

Mark Clipsham.