Qpump is working hard to push oil in a small area.... Q
And lot of oil moving out the closed side creates high back pressure. With 11gpm in, there is 15-25 gpm going out CL side. This effect is more pronounced with smaller diameters, as the ratio of closed side area to rod side area is much larger.
Then, this higher psi back pressure is applied to a larger area so the force is quite high. Rod side area then needs higher pressure to push the piston.
It is a strange effect, not 'common sense' maybe, but a servo valve and cylinder circuit, or any circuit that becomes pressure limited instead of flow limited, will retract the rod SLOWER than it extends.
Put a gauge in it, if the pressure is too high the pump is probably unloading to low speed, or if really bad might be going across the relief valve.
If it is a problem, you could try larger return hoses, larger return filter, larger valve, or in extreme cases a pilot operated valve from closed side right back to tank. There was an earlier post about a larger Timberwolf splitter that may use this circuit.