I have replaced a toilet with a new Foremost Dual flush mode toilet. When I installed the tank I cannot seem to tighten the bolts enough so that the tank has no movement towards the wall. It seems to me that the toilet came with a rubber bushing that installs between the base and the tank. This bushing is where the water exits the tank and enters the base. The bushing seems to be what is not allowing the tank to sit flush on the base. The toilet does not leak at all. If I tighten the bolts any more I am afraid to break the toilet.
If you cannot tighten them much more by hand then don't do it - I've cracked a toilet tank by overtightening because one side seemed to insist it be higher than the other side. . . believe me, once there's tension it doesn't take much more - just one more twist - and then CRACK!
So - I think you should consider giving the back resistance from behind - How possible would it be to remove the tank and install a series of shims or a thin layer of wood to the wall behind it to "move" the wall forward and make contact - thus - taking away the wiggle room?
At this present moment in time I am making cabinets for the kitchen - just in case you wanted to know what I'm doing when I'm not around.
I was thinking the same thing. But I cannot beleive that the product is so poorly designed. I am going to go back to the store and see if they have any ideas or are will to get support from the manufacturer.