I can understand why you would want that SWR lower, but there's nothing wrong with a 1.3:1.
I'm curious, are you adjusting that shorting strap 'around' those coil turns, or just straight up/down? The straight up/down is a 'coarse' adjustment, the 'around' thingy is a fine adjustment.
That insert to keep the tubing from being crushed isn't going to make any difference if it isn't making a contact it shouldn't make, I sort of doubt if it is.
The biggest difference when moving an antenna is that you are changing it's reactance with what's around it. Height means that's with the dirt under it. That is normal for any antenna, sometimes it makes a big difference, sometimes not (figure on it making a difference). You can use that, it isn't always a detriment! One way is by the 'angle of the dangle' of those radials. Seeing how they are attached, that may not be an easy thing to manage, or even wanting to do it. It certainly isn't a sure 'cure', so think about it before doing it. If you're not sure of getting it back like it was, I think I'd pass on that option. If they aren't already, try shorting them to the mounting post. Might work, can't hurt.
So far it sounds like things are about 'normal'. What would really be bizarre is if it didn't change!
- 'Doc
(There's a lot of things in here that I figure you already know, it's just that I don't know if you do or not. I'm not trying to be insulting, I do insults a lot better than that!)