There is a formula somewhere that says for a certain size pipe @ x gal per min. add so much head per lineal foot. I can't find it right now.
I'm sure it is on the web some where. I will look for all my notes later today. I know from experience that for 3/4in tubing @ 600-800gal per min you have to add like 3ft of head for every 10 lineal feet. I learned the hard way but that is an off topic disc.
Also, You can only fit so much water through that tube which I'm guessing is 1/4in O.D. At some point you will reach the maximum flow rate of the tubing.
My point is that 1/4in tubing is a hell of a lot more restrictive than 3/4(I know Duh
stating the obvious) . If you think about it this way, you may be asking your pump to push more like 20' of head. Not to mention, through a little opening. Uphill both ways in the snow with no shoes on...