Laying limestone slabs on block and beam patio

[Jerryscotch]

I plan to lay 600mm wide/random length, 22mm thick limestone slabs, on to a block and beam raised patio that I built last year.

The blocks have not yet been grouted - that's happening next. The span is fairly small - 3.4m, but I notice a fairly small deflection/vibration if you lower your weight down from tip toes, at the mid-point.

Firstly, is this deflection likely to be eliminated once the slabs, plus 50mm bedding layer have been applied? and, if not, would anyone advise any modification to 1: 5 cement/grit sand that I was thinking of using?

Secondly, would an SBR bonding layer applied directly to the concrete block and beam base, prior to laying the flags, in addition to the flag/mortar bond bridge be advisable?

I really don't want these to move!