You might be right, but the OP states that a 10mm tile will create a lip above the tray, so I would guess the vinyl would be close to level. Still, maybe no fall towards the tray, but might be easier to take the flooring up, if it is already laid, and create the right levels, than raising the...
Is it possible to use a clear floor sealer over the Karndean to create a floor surface capable of preventing water ingress?
Like this shit maybe, but clear? http://www.reprotecuk.co.uk/products/reprotec-flexiflor
Contractually, if the absence of shower screen is specified, i.e. no screen is...
Note that the OP, despite the numerous problems the client is giving him, is remaining with the project and trying to resolve the problems and not just bailing out.