how to make a fence join with a custom block

I have created a 16 x 8 quartz panel and I have made a quartz fence that I made following a tutorial from the same mcreator, the thing is that the fence does not join my quartz panel but it does with a solid block of 16 * 16, how can I make the fence join my quartz panel, any help please. 

Here you can see how it does not join my quartz panel, but it does with a solid block of 16*16

https://postimg.cc/wybjN0jH