Help with Mining on RTX 2080

Hi guys, I'm new to mining so sorry if any of this is stupid questions. I've been looking around online at what hashrates people have been getting with the RTX 2080 and it looks like its around 28 MH/s and I start out there when I launch my miner (T-Rex v0.20.0) but it always steadily drops and stabilizes around 21-22 MH/s. Any ideas as to what I might be doing wrong? I've linked a screenshot of settings and the hashrate below.
https://imgur.com/a/C8Tm4Np