Hmm that's strange but could this be down to the brand? The 15mm I have coming are second hand and have been fitted so with any luck they'll go right on. Did you try sanding your hubs a little or using a wire brush? Perhaps caked on brake dust was preventing it?
The 10mm H&Rs went on perfectly, slipped right on and they sit flush. I don't blame you with the jack, I hate the OE jack, it's very dangerous and especially with coilovers. I have found that because the shock absorbers are shorter and stiffer, when you jack up one wheel, the other wheel on the opposite side lifts from the ground also which will make the car fall off of the jack. If I could get hold of another OE jack, it would be a lot safer.
I have two different pairs of spacers from two different sources/brands, neither would go all the way onto the hub. Didn't try cleaning the centre bit of the hub for fear of knocking the car off the jack but will be getting a trolley jack come payday and having another go soon so will try that, Lee did suggest that too. There did seem to be a bit of gunk on them, not quite like brake dust, more like some sort of grease - i seem to remember reading or hearing somewhere that this was necessary on the hub face which meets the wheel?