Planting under PINE TREES

Hi all, I’m having issues with getting my escalonias to grow along my back fence, approx 60m. The same plants are doing well along the side fences. All get the same water, but the ones along the long back fence are suffering.

The fence is on the north east side, so the pine trees block alot of the winter sun, and I’m guessing also steal all the water from the escalonias.

I have recently added the mulch about 2 months ago. Coming into winter now I’m not expecting much growth even with the mulch holding in the moisture.

Is there something I can do to boost their growth, or am I fighting a loosing battle to the pines?? Is there an alternative screening plant that would do better here? Thank you