Hephestos Bed Level

I've just built a Prusa i3 Hephestos and it's really cool. I've done a few test prints and played with some settings and am making some progress. The one thing that I still think isn't 100% is the bed level. I find it difficult to get the first layer or so to stick to the bed (I'm using blue painters tape on non heated glass bed and printing PLA). When I have done, there is some lifting, mainly on the left hand side looking at the model.

To level the bed, I made sure the X Axis was level using little spirit level and manually adjusted on the threaded rods. I then went through the bed level process on the printer software and managed to get each corner at the recommened Z height (using a piece of paper) but when the exruder moves to the middle of the bed at the end, the gap is higher. I feel that this is the cause or at least not helping.

Is this normal? I don't see why the centre should be out if the corners are all consistent. Also, after levelling, a spirit level across the bed shows that it is slightly down on the left hand side. Is there anything I'm missing or can try to make the bed more level?

I had same thing except either left or right side too high in the past. The recent bed tramming I did was about 1-2 month ago, gone quite to the extreme method of doing 5 passes to ensure bed are perfectly leveled and measured with piece of paper.

I would recommend use the guide from reprap wiki on how to adjust your bed level. Basically best way to do it is by adjusting screws diagonally, first diagonal would be front left with rear right, and second diagonals would be rear left and front right.

Probably you should try to add auto bed leveling

My main problem I always have is the height of bed. People kept telling me to solve the problem, yet it kept coming again and again. I've been adjusting z home offset (this is overall, not specific point) so I don't have to adjust the endstop trigger