Paving nightmare

[Mojooo]

So I am trying to lay some paving slabs in the garden - I've already done a lot of the hard work in taking up the old slabs and putting in a base.

The slabs are indidian sandstone so all different thicknesses and the surfaces are not perfectly flat.

My difficulty is when I put the slab down initally I am finding it very difficult to get it at the right level (to match a brick course of my house) - once I start using a mallett to adjust levels of the falls - I can never get it right - either the slab doesn't move enough or if you hit it too much one way it buggers the level the opposite direction.

I have tried various mortar (sharp sand and cement) strengths (4 in 1 and now 6 in 1) and different water volumes from a dry mix to a wet mix. I found with the wet mix when I was using the mallett to hit the slab down it was eventually causing water to rise up.

I think I need to try and get the bed of mortar perfect before I put the slab on.

Any tips on how to resovle this before I throw the towel in?

[Mojooo]

I am using a full bed.

I am doing the troughs but maybe I need to make them a bit deeper.

I looked into using an additive but I thought I read that they were fine for bricklaying mortar but not so much for paving as the sharp sand makes less likely to work. I understand admix or whatever makes bricklaying mortar more workable so what can I use withsharp sand?