Lilly pilly hedges growing unevenly

Question

I have 12 lilly pilly (acmena smithii) hedges (2 out of picture) facing south in the Victoria, Australia which get some sun all year round. It seems though that the ones on the left are growing much better and they degrade off in size going right. Would the tree on the other side of the fence be playing a part in that? They were planted late march 2017 and have bushed out quite a bit, I've been trimming regularly up until about 2 months ago.

I've put some seaweed fertiliser on them last month to give them a feed before we hit winter in june.

So my questions are:

• Is the size difference just a thing that happens or should I be doing something to the smaller ones to encourage growth?
• How often should I trim the tops of these, 1-2 year? Or way more often? My end goal is for them to be just under 2m in height.

Answer 1

Prune them 1 inch each side looks like yours hasn't been pruned much. I would have pruned on 1inch off of all Lilly Pillies and 2 inches off of big one. Do it on ok weather not on a super hot day

Answer 2

Too late now, but the Melaleuca behind would suppress growth. Particularly noticeable with the same plants in a row.