ice formation on heat pump

Hi there
hope everybody is fine.
I have a problem with an heat pump.
the coil is working as evaporator and the condenser is water cooled.
Following is the problem
This heat pump is working @ 44.6/42.8 F DB/WB and should evaporate @ 27F
what happens is that the evaporation temperature is dropping @ 22F and I am noticing in the bottom part of the coil an ice formation.
More specifically, the band of ice appears first at 1/4 of the coil, starting from the bottom, and then expands to all the bottom part - that is from 1/4 of the coil to the bottom.

I deem the two elements are not correlated, even though it is logic that there is ice formation since of low temperatures.
My point of view is that the coil is underdimensioned, nonetheless the frost formation in the sole bottom part may be an indicator of bad refrigerant distribution.
One possible action could be increasing the air flow, or asking if the coil has been sized correctly (distributor, number of circuits)
Please, which is your experience with this kind of issues ?
Many thanks