Self-levelling floor compound

Okay, I've just put some of this stuff down on my new shower room floor about a week ago - unfortunately I think I might need some more :it doesn't cover my heating cable completely *and* my floor was more unlevel than I thought :( , so two questions.
1. Is it safe to put another layer of the stuff on a previously dried layer (of about 5mm)
2. Related tot ge 1st question; on the two brands I am aware of : B & Q value and Febfloor, they both say you shouldn't put it on any thicker than 5-6mm or (as the B & Q suggests), you need to add granite chippings. Now is that per application or the maximum regardless of th enumber of layers. For example I alreday have a dried layer of 5mm, so I suppose I'm asking the same as the first question - can I put another layer on top of this ?
TIA Steve
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