$BOOT_PARTITION : No space left on device

This is a Motorola Moto G6.

There were few work arounds that I had to do to get to where I am right now. But I've come up on to an issue which I am not able to solve my self. I am using the testing port and followed the install guide. Using a non-official twrp image which I assume will allow me to install 64bit images (used official twrp which stops saying zip verification failed or something similar).

I am doing a android-recovery-zip type of installation where I sideload zip file using adb. Device shows that its flashing boot.img followed by Failed ....

I've Inspected the /tmp/pmos.log. It says,

dd: error writing '/dev/block/mmcblk0p36': No Space left on device
45057+0 records in 
45056+0 records out

Further inspections lead me to find out that /dev/block/mmcblk0p36 is the boot partition

Then the next time I initialized using pmbootstrap init I increased boot size to 750mb, just to see where it goes.

[17:41:57] Additional options: extra free space: 128 MB, boot partition size: 256 MB, parallel jobs: 3, ccache per arch: 5G, sudo timer: False
[17:41:57] Change them? (y/n) [n]: y
[17:41:59] Set extra free space to 0, unless you ran into a 'No space left on device' error. In that case, the size of the rootfs could not be calculated properly on your machine, and we need to add extra free space to make the image big enough to fit the rootfs (pmaports#1904). How much extra free space do you want to add to the image (in MB)?
[17:41:59] Extra space size [128]: 1024
[17:42:05] What should be the boot partition size (in MB)?
[17:42:05] Boot size [256]: 750

Even though I increase this size, it doesn't seem to increase the /dev/block/mmcblk0p36 size it stays the same. I verified by checking /proc/partitions file.

Is there anyway to increase this partitions size? Or am I doing something wrong somewhere?