I don’t have any experience with that Arcam, but I do have previous experience with a NAD that used DIRAC. I actually found decent results with the DIRAC mic (and later UMIK) taped and used/slotted (UMIK) to a mic stand. The mic stand provided better stability, quicker height adjustability, and better accuracy for the position sweeps. Vertical was recommended since you’ll be measuring the room. Mic pointed towards the speaker not recommended since you would then be measuring the speaker. I had mixed results with DIRAC, but ultimately found that the accuracy (and subsequently results) of DIRAC were dependent on the quality of the sweeps. The vertical and lateral mattered - at least it did for me. Below is what I used: