I am sorry, I meant flow by piston like Mk2. My point is that the pressure changes are not a function of the size of the piston head. A different size piston head, )like the Mk3 or Mk200 is compensated for with a different strength spring and the IP drop is unchanged.
I think I know what you mean, but for me is the static IP and the IP difference between full and near empty tank the result of the work force of the sealing force of the piston on the one hand
and the resisting forces of the spring force and the supply pressure force ( and maybe some friction force of the piston o-rings) on the other.
If you change one of those factors, the IP or the IP difference will change.
If you want that the IP to 'behave' like in the old configuration you would have to modify the other factors as well.
Like I think that making the orifice bigger to produce a higher flow demands a slightly bigger piston head and a spring which produces a little bit less counter force (by taking away a shim for example) to produce the same IP qualities as before, so I think to reduce effect of the supply pressure (less variance of IP) one would have to make the orifice smaller and strengthen the spring (or accept more shims) and keep the same piston head size.
But that would mean that the flow characteristics (output) would be reduced.
My major point (understanding) is that these opposing forces (sealing force versus spring force and supply pressure force) produce the IP and its characteristics over the course of the supply spectrum range and if you change one factor then you have to adapt the other factors to achieve the same IP qualities as before.
I must admit I'm still not 100% sure that what I wrote is absolute correct, but the idea that if I change the size of the orifice I have only to change the spring pressure ( what you have to do to my opinion anyway) to achieve the same IP drop doesn't make much sense to me.
