Playing slide guitar in standard tuning is difficult. Because you’re not in an open tuning the overtones sound terrible if you’re not damping properly.
In open tuning you can have overtones ringing and they’re in tune because the guitar is tuned to a chord.
The important thing is not to get discouraged. It sounds like crap in the beginning for everyone. When someone has been playing slide/bottleneck in standard tuning for years it looks and sounds easy. It’s not.
I started playing slide/bottleneck in open tunings and it wasn’t until I was at a friends gig and hear him playing in the key of G in standard tuning that I really got interested in it.
One of the many benefits of playing slide/bottleneck in standard tuning is you don’t have to re-tune the guitar. You can just improvise on the fly. It takes some practice but once you get the damping and intonation down the fretboard is wide open.
The Video advertised above mine is one I own and recommend because it shows the old guys playing. Because they are all gone now we can’t see them in concert. This is the next best thing.