I have a Challenge too. Totally depends on what you are shooting and what you want to achieve. You said it's HFT so is that UKAHFT (45 yards) or further for regional rules? Do you have the Steyr rail (or any rail fitted), do you need to add MOA ?
If standard 45 yard HFT the old rule of thumb was low to the barrel but going slightly higher can push out your 'sweet spot'. Depends a bit on your ability to range find.
Need more info basically.
Steyr Challenge HFT - HW97K - BSA Mercury Challenger - Anschutz 9015 One - AA Pro Target - AA Pro Elite - ASI Paratrooper (R) - Walther LP500