The dreaded "SAMEPERIODLASTYEAR" Function

Hi Guys - I was wondering if someone could perhaps help....  I've spent a day on this, read just about every forum post, but I'm clearly missing something in relation to the SAMEPERIODLASTYEAR function.

Details:

I have a Transaction DB - Consumed into PowerBi via Odata

I have a seperate Calendar DB I created in PowerBi (Well formed)

On the transaction DB - I have created the following measures:

Sum of Sales -->  Sum of Sales = SUM (Transactions[amount])

Year to Date Sum of Sales -->  YTDSumOfSales = TOTALYTD([Sum of Sales],'CALENDAR'[Date])

Last Year Sales -->  SalesLastYTD = CALCULATE([YTDSumOfSales], SAMEPERIODLASTYEAR('CALENDAR'[Date]))

For some reason the Last Year Sales Measure is moving the measure ahead; instead of behind (IE - 2018, insted of 2016) - Here is what the table of the data looks like the below.

Essentially I am trying to create some KPI Scorecards to show you how you are trading against Last YTD / Last MTD / Last WTD / This Week vs Last Year This Week / Today vs Today Last Year.

Any direction would be well recieved!