Risk Management – Variable Position Size

Hi everyone,

I have a question regarding my PRT Code.  I wanted to define the position size so that the same risk in terms of $ value applies for each trade. Once I perform a backtest the position size varies and most of the time it is doing what it should. But there is also a significant number of exceptions where the result deviates too much from the original intention with 1:1 Risk/Reward.

Please find below the code and attached also a picture of the results with yellow marked deviations.

SL = (High - Low)
R = 500
Tickvalue = 2
OrderQty = Round ((R / SL) / Tickvalue),0)

//Conditions for Direction Short
IF .... THEN
Direction = -1
ENDIF

IF NOT OnMarket AND Direction = -1 THEN
SELLSHORT OrderQty CONTRACT AT (Low - 0.25*pipsize) Stop
SET STOP PLOSS (SL)*pipsize
InitialSL = SL
ENDIF

//Exit Short 1:1
IF ShortOnMarket THEN
SET STOP PLOSS (1*InitialSL)
SET TARGET PPROFIT (1*InitialSL)
ENDIF

The average position size is like 10-15 contracts, so it is not the problem that it is only 1 contract.

What is wrong in my code and what can I do better in order to have a proper position size for risk/reward calculation?

Thank you very much for your support.

Best regards

Simon