SDR# Frequency Scanner sensitivity

[Jonnywithacamera]

I use SDR Sharp with the frequency scanner plugin to monitor MilAir UHF frequencies. I am unclear the differences between the red line with red arrow buttons and the “detect” setting. I’d like to get my scan as sensitive as possible to maximum range without picking up junk/static. I currently have detect on 55 and put the red line down as far as possible without getting static. Any clarification on this? Are there other ways to get better range? I use the DPD Productions 225-400 MHZ car antenna and have it propped up as high as possible inside of my house

 

[Saint]

This is what I have.
Saint