Shower trap drainage

Due to other issues I have a very waste pipe that runs virtually level under my tray until it runs into stack.

On testing it worked perfectly well although I'm left with slightly more water in the trap than I should have.

Should I look to replace the rap with a shallow version such as the one in the link, as this may introduce a small fall.

Is the fact there's water in the pipe likely to cause issues down the line?

http://www.screwfix.com/p/wirquin-pro-slim-high-flow-shower-waste-90mm/10400

Cancel that, on closer inspection although the fall is minimal, the trap water level is due to its design,

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