XMedia Recode - Video Tab - "Preset" Setting

[Cherry Picker]

This question is in regards to XMedia Recode and the "Preset" setting on the video tab (not the "Profile" setting on the initial Format tab). I've recoded dozens of videos without issue but the most recent two produced a "Format Not Supported" error on my TV (Samsung 6 Series). PC and Phones play without issue though. After recode testing with various settings, I finally found the issue. It was the "Preset" button on the video tab.

I usually always set it to "Medium" or "Slow", but this time I used "Slower":


[Attachment 62599 - Click to enlarge]

After recoding again on "Slow" the TV played them fine.

My recode approach is generically the same each time:
- Output is always h264
- On the initial "Format" tab, it's always "Custom" Profile h264
- Always 2 Pass
- Frame Rate keep Original
- Bit Rate I'll adjust to Original

I'm OK with recoding at "Slow" or higher now that I know the TV will support. My question is a generic one regarding what this "Preset" setting actually does. I know that encoding times are longer the slower it is set.

1 - I thought the slower the preset, the better quality - is this incorrect? (Quality is my primary concern over time or file size).
2 - Maybe the slower the preset, the tighter the compression - which is why my TV device choked? It was too much compression?
3 - I wonder how this setting affects the relationship between file size/encoding time/quality.

Thanks all.